Algebra: Ratio Word Problems

Related Pages Two-Term Ratio Word Problems More Ratio Word Problems Algebra Lessons

In these lessons, we will learn how to solve ratio word problems that have two-term ratios or three-term ratios.

Ratio problems are word problems that use ratios to relate the different items in the question.

The main things to be aware about for ratio problems are:

  • Change the quantities to the same unit if necessary.
  • Write the items in the ratio as a fraction .
  • Make sure that you have the same items in the numerator and denominator.

Ratio Problems: Two-Term Ratios

Example 1: In a bag of red and green sweets, the ratio of red sweets to green sweets is 3:4. If the bag contains 120 green sweets, how many red sweets are there?

Solution: Step 1: Assign variables: Let x = number of red sweets.

Step 2: Solve the equation. Cross Multiply 3 × 120 = 4 × x 360 = 4 x

Answer: There are 90 red sweets.

Example 2: John has 30 marbles, 18 of which are red and 12 of which are blue. Jane has 20 marbles, all of them either red or blue. If the ratio of the red marbles to the blue marbles is the same for both John and Jane, then John has how many more blue marbles than Jane?

Solution: Step 1: Sentence: Jane has 20 marbles, all of them either red or blue. Assign variables: Let x = number of blue marbles for Jane 20 – x = number red marbles for Jane

Step 2: Solve the equation

Cross Multiply 3 × x = 2 × (20 – x ) 3 x = 40 – 2 x

John has 12 blue marbles. So, he has 12 – 8 = 4 more blue marbles than Jane.

Answer: John has 4 more blue marbles than Jane.

How To Solve Word Problems Using Proportions?

This is another word problem that involves ratio or proportion.

Example: A recipe uses 5 cups of flour for every 2 cups of sugar. If I want to make a recipe using 8 cups of flour. How much sugar should I use?

How To Solve Proportion Word Problems?

When solving proportion word problems remember to have like units in the numerator and denominator of each ratio in the proportion.

  • Biologist tagged 900 rabbits in Bryer Lake National Park. At a later date, they found 6 tagged rabbits in a sample of 2000. Estimate the total number of rabbits in Bryer Lake National Park.
  • Mel fills his gas tank up with 6 gallons of premium unleaded gas for a cost of $26.58. How much would it costs to fill an 18 gallon tank? 3 If 4 US dollars can be exchanged for 1.75 Euros, how many Euros can be obtained for 144 US dollars?

Ratio problems: Three-term Ratios

Example 1: A special cereal mixture contains rice, wheat and corn in the ratio of 2:3:5. If a bag of the mixture contains 3 pounds of rice, how much corn does it contain?

Solution: Step 1: Assign variables: Let x = amount of corn

Step 2: Solve the equation Cross Multiply 2 × x = 3 × 5 2 x = 15

Answer: The mixture contains 7.5 pounds of corn.

Example 2: Clothing store A sells T-shirts in only three colors: red, blue and green. The colors are in the ratio of 3 to 4 to 5. If the store has 20 blue T-shirts, how many T-shirts does it have altogether?

Solution: Step 1: Assign variables: Let x = number of red shirts and y = number of green shirts

Step 2: Solve the equation Cross Multiply 3 × 20 = x × 4 60 = 4 x x = 15

5 × 20 = y × 4 100 = 4 y y = 25

The total number of shirts would be 15 + 25 + 20 = 60

Answer: There are 60 shirts.

Algebra And Ratios With Three Terms

Let’s study how algebra can help us think about ratios with more than two terms.

Example: There are a total of 42 computers. Each computer runs one of three operating systems: OSX, Windows, Linux. The ratio of the computers running OSX, Windows, Linux is 2:5:7. Find the number of computers that are running each of the operating systems.

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Here you will learn about ratios, including how to write a ratio, simplifying ratios, unit rate math and how to solve problems involving ratios and rates.

Students will first learn about ratios as part of ratios and proportions in 6 th grade and 7 th grade.

What is a ratio?

A ratio is a multiplicative relationship between two or more quantities.

Ratios are written in the form a : b, which is read as “a to b”, where a and b are normally integers, fractions, or decimals.

The order of the quantities in the ratio is important.

For example,

If there are 10 boys in a class and 15 girls, the ratio of boys to girls is 10 : 15 which is read as “10 to 15.” This is an example of a part to part ratio. You could also say the ratio of total students to girls is 15 : 25. This is an example of a part to whole ratio.

Step-by-step guide: How to write a ratio

Since a ratio represents a relationship, there is always more than one way to show it.

This includes unit rate math – which creates equivalent ratios where one part of the ratio is 1.

You can use unit rates to compare different quantities.

A grocery store sells a bag of 6 bananas for \$ 2.34 and a bag of 4 bananas for \$ 1.44.

Which bag has the better unit price?

Unit price means the price per 1 unit. In this case, the units are bananas. Divide each ratio to find the price for 1 banana.

Ratio Image 1 US

The bag of 4 bananas is \$ 0.36 per banana, which is cheaper than the bag of 6 bananas which is \$ 0.39 per banana.

Step-by-step guide: Unit rate math

Unit rates are not the only types of equivalent ratios. When simplifying fractions, use the common factors to divide all the numbers in a ratio until they cannot be divided further to write the ratio in lowest terms.

The ratio of red counters to blue counters is 16 : 12.

Ratio Image 3 US

You can simplify the ratio to lowest terms by finding the greatest common factor \textbf{(GCF)} of each of the numbers in the ratio.

Factors of 16 \text{:} \, 1, 2, 4, 8, 16

Factor of 12 \text{:} \, 1, 2, 3, 4, 6, 12

The greatest common factor is 4. To simplify the ratio, you divide both sides by 4.

Ratio Image 4 US

Step-by-step guide: Simplifying ratios

Another way to write ratios is by using fraction notation.

Fraction notation can be used to show a part to whole ratio relationships.

The bar model below shows the ratio of blue : red as 3 : 2 (3 to 2). There are 3 blue blocks, 2 red blocks and 5 blocks in total.

Ratio Image 5 US

This part to whole relationship allows us to make statements like…

  • \cfrac{3}{5} of the blocks are blue
  • \cfrac{2}{5} of the blocks are red
  • \cfrac{5}{5} of the blocks are blue or red

The ratio of blue : red as 3 : 2 can also be shown as a part to part fraction…

Ratio Image 6 US

The fractions show the ratio relationship BETWEEN the blue and red blocks. This allows us to make statements like…

  • The number of blue blocks is \cfrac{3}{2} larger than red
  • The number of red blocks is \cfrac{2}{3} the amount of blue

Step-by-step guide: Ratio to fraction

Ratios can also be written with percents.

Ratio Image 7 US

The ratio of pencils to crayons is 4 : 6.

The ratio has 10 parts, so the fractions are

\cfrac{4}{10} : \cfrac{6}{10}.

The numerator represents the numbers of the ratio, which show how many pencils or crayons there are. The denominator represents the total number of pencils and crayons.

You may be able to recognize what the fractions are as percents or you may need to use long division to help convert your fractions.

\cfrac{4}{10}=40 \%, so 40 \% are pencils.

\cfrac{6}{10}=60 \%, so 60 \% are crayons.

Step-by-step guide: Ratio to percent

Solving problems with ratios is common in the real world. One place that this shows up is in calculating exchange rates. An exchange rate is the rate at which the money of one country can be exchanged for the money of another country.

Using a currency’s exchange rate you can convert between US dollars and foreign currencies.

To convert from US dollars (USD) to Japanese yen (JPY), you must multiply by the exchange rate.

Ratio Image 8 US

So \$ 15 \; USD would be ¥2,134.35 \; JPY because,

\$ 15 \; USD \times 142.29=¥ 2,134 .35 \; JPY.

Step-by-step guide: How to calculate exchange rates

All the skills above are examples of ratio problem solving. When solving problems with ratios, it is important to ask:

  • What is the ratio involved?
  • What order are the quantities in the ratio?
  • What is the total amount / what is the part of the total amount known?
  • What are you trying to calculate ?

In the classroom, ratio problem solving often comes in the form of real world scenarios or word problems.

\cfrac{8}{10} students are right handed. What is the ratio of left handed students to right handed students? (2 : 8)

Step-by-step guide: Ratio problem solving

What is a ratio?

[FREE] Ratio Worksheet (Grade 6 and 7)

Use this quiz to assess your 6th and 7th grade students’ understanding of ratios. Covers 10+ questions with answers on ratio topics to identify areas of strength and support!

Common Core State Standards

How does this relate to 6 th grade math and 7 th grade math?

  • Grade 6 – Ratios and Proportions (6.RP.A.1) Understand the concept of a ratio and use ratio language to describe a ratio relationship between two quantities. For example, “The ratio of wings to beaks in the bird house at the zoo was 2 : 1, because for every 2 wings there was 1 beak.” “For every vote candidate A received, candidate C received nearly three votes.”
  • Grade 6 – Ratios and Proportions (6.RP.A.2) Understand the concept of a unit rate \cfrac{a}{b} associated with a ratio a : b with b ≠ 0, and use rate language in the context of a ratio relationship. For example, “This recipe has a ratio of 3 cups of flour to 4 cups of sugar, so there is \cfrac{3}{4} cup of flour for each cup of sugar.” “We paid \$ 75 for 15 hamburgers, which is a rate of \$ 5 per hamburger.”
  • Grade 6 – Ratios and Proportions (6.RP.A.3) Use ratio and rate reasoning to solve real-world and mathematical problems, for example, by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
  • Grade 6 – Ratios and Proportions (6.RP.A.3b) Solve unit rate problems including those involving unit pricing and constant speed. For example, if it took 7 hours to mow 4 lawns, then at that rate, how many lawns could be mowed in 35 hours? At what rate were lawns being mowed?
  • Grade 7 – Ratios and Proportions (7.RP.A.1) Compute unit rates associated with ratios of fractions, including ratios of lengths, areas and other quantities measured in like or different units. For example, if a person walks \cfrac{1}{2} mile in each \cfrac{1}{4} hour, compute the unit rate as the complex fraction \cfrac{\cfrac{1}{2}}{\cfrac{1}{4}} miles per hour, equivalently 2 miles per hour.

How to work with a ratio

There are a lot of ways to work with a ratio. For more specific step-by-step guides, check out the ratio pages linked in the “What are ratios?” section above or read through the examples below.

Ratio examples

Example 1: how to write a ratio.

Ratio Image 9 US

Write the ratio of apples to pears.

  • Identify the different quantities being compared and their order.

There are 5 pears and 2 apples.

The order of the ratio is apples to pears.

2 Write the ratio using a colon.

Apples : Pears

\hspace{0.7cm} 5 : 2

3 Check if the ratio can be simplified.

5 and 2 only have a common factor of 1, so this ratio is already in its lowest terms (simplest form).

Example 2: unit rate calculation – decimal

A car travels 303 miles in 6 hours. If the car travels the same number of miles each hour, what is the miles per hour rate?

Write the original rate.

303 miles in 6 hours → 303 : 6.

Use multiplication or division to create a unit rate.

The miles ‘per hour’ refers to 1 hour. Divide each side of the rate by 6, to create a rate for 1 hour.

Ratio Image 10 US

Use the unit rate to answer the question.

The car travels 50.5 miles each hour.

Example 3: simplifying ratios

Write the ratio 48 : 156 in lowest terms.

Calculate the greatest common factor of the parts of the ratio.

Factors of 48=1, 2, 3, 4, 6, 8, 12, 16, 24, 48

Factors of 156=1, 2, 3, 4, 6, 12, 13, 26, 39, 52, 78, 156

GCF(48,156)=12

Divide each part of the ratio by the greatest common factor.

Ratio Image 11 US

4 : 13 is in lowest terms.

Example 4: solving a problem involving ratio to percents

The ratio of adults to children in a park is 11 : 14.

One-fourth of the adults are women. What percent of the people in the park are men?

Add the parts of the ratio for the denominator of the fractions.

11+14=25. There are 25 parts in total. The denominator is 25.

Convert each part of the ratio to a fraction.

11 : 14 becomes \cfrac{11}{25} : \cfrac{14}{25}.

Convert the fractions to percents.

\begin{aligned}& \cfrac{11}{25}=\cfrac{44}{100}=44 \% \\\\ & \cfrac{14}{25}=\cfrac{56}{100}=56 \%\end{aligned}

You now know that 44 \% of the people are adults.

One-fourth of the adults are women.

\cfrac{1}{4} of 44 \%=11 \%.

11 \% of the people in the park are women and therefore 44-11=33 \% of the people are men.

Example 5: converting from KRW / USD

₩5,000 \; KRW is equal to \$ 3.85 \; USD. What is the exchange rate from \$ \; (USD) to ₩ \; (KRW)?

Use the information given to set up a rate.

When calculating the currency exchange rate from ₩ \; (KRW), you want to know how many ₩ \; (KRW) are equal to \$ 1 \; (USD). This is the ratio of ₩ to \$, so set up the rate as \cfrac{₩ 5,000}{\$ 3.85}.

Divide both parts by the base currency.

In this case, the base currency is \$ \; (USD), so divide both parts by 3.85, rounding the ₩ \; KRW is to the nearest whole:

\cfrac{₩ 5,000 \div 3.85}{\$ 3.85 \div 3.85}=\cfrac{₩ 1,299}{\$ 1}.

State the final exchange rate with the correct currency symbols.

The exchange rate from \$ \; (USD) to ₩ \; (KRW) is 1,299.

Example 6: ratio problem solving – mixed numbers

Fruit Salad Recipe:

  • 2 \cfrac{1}{2} cups of blueberries
  • 2 \cfrac{1}{5} cups of orange slices
  • 1 \cfrac{1}{4} cups of strawberries
  • 2 cups of apple slices

Write the ratio of the total cups of berries for every 1 cup of strawberries in the salad.

Identify key information within the question.

There are 1 \cfrac{1}{4} cups of strawberries and 2 \cfrac{1}{2} cups of blueberries.

Know what you are trying to calculate.

You need to create the ratio of the total cups of berries (strawberries and blueberries) for every 1 cup of strawberries.

Use prior knowledge to structure a solution.

First add 1 \cfrac{1}{4}+2 \cfrac{1}{2} to find the total cups of berries.

\begin{aligned}& 1 \cfrac{1}{4}+2 \cfrac{1}{2} \\\\ & =\cfrac{5}{4}+\cfrac{5}{2} \\\\ & =\cfrac{5}{4}+\cfrac{10}{4} \\\\ & =\cfrac{15}{4}\end{aligned}

Then write the ratio of total cups of berries to cups of strawberries.

\cfrac{15}{4} : \cfrac{5}{4}

Now multiply both sides of the ratio by \cfrac{4}{5}, to calculate the ratio of 1 cup of strawberries.

\cfrac{15}{4} \times \cfrac{4}{5} : \cfrac{5}{4} \times \cfrac{4}{5}

There are 3 total cups of berries for every 1 cup of strawberries.

*Note: To solve, you can also write the ratio \cfrac{15}{4} : \cfrac{5}{4} as the complex fraction \cfrac{\cfrac{15}{4}}{\cfrac{5}{4}} and find the quotient of the numerator and denominator.

Teaching tips for ratio

  • There are many ways to engage students in ratios. One way is to introduce the golden ratio (based on Fibonacci’s sequence) and challenge students to look for it in the real world. Keep a chart or wall in the classroom for students to add any examples of this ratio that they find.
  • Incorporate as many examples of ratios in the classroom as you can – even across subjects. For example, have students write ratios about the “Word of the day” – from an English or Science class. Such as “Write the ratio of nouns to adjectives” or “Write the ratio of words with the letter ‘e’ to total words.”
  • As students work with ratios in different ways, keep track of successful solving strategies on a bulletin board or on chart paper. This allows students to see and utilize another students’ strategy, make connections between strategies and feel ownership in any ideas they help create.
  • Be mindful of how to progress with ratio topics. Typically whole number ratios are introduced first, then ratios with rational numbers. Ratios that involve compare only fractional (or decimal values), such as \cfrac{2}{3} : \cfrac{5}{6} or 0.45 : 0.34 are the most difficult for students. As always, be mindful of your state’s curriculum when making decisions on when to introduce certain ratio topics.

Easy mistakes to make

  • Writing the ratio in the wrong order A common error is to write the parts of the ratio in the wrong order. For example, The number of dogs to cats is given as the ratio 12 : 13 but the solution is incorrectly written as 13 : 12.
  • Confusing ratios and fractions You can write a ratio with fraction notation. A part to whole fraction will have the same fractional language as a fraction. However, a part to part fraction will not. For example, The ratio of boys to girls is 2 : 3. Two ways to express this ratio are \cfrac{2}{3} or \cfrac{2}{5}. However, you must be careful how you read these fractions. You can say “ \cfrac{2}{5} of the kids are boys” but you cannot say “ \cfrac{2}{3} of the kids are boys.” Instead, say “The number of boys is \cfrac{2}{3} the number of girls.”
  • Not fully simplified A common error is to not find the greatest common factor when simplifying a ratio. For example, Simplify the ratio 12 : 18. Dividing both numbers by only 2 leaves a ratio of 6 : 9, which is not fully simplified. This can be simplified further by dividing by 3 to get the ratio 2 : 3, which is the correct answer. By dividing both numbers by the greatest common factor, 6, would get the ratio 2 : 3 in one step.

Practice ratio questions

1. 500 people attended a concert. There were 240 boys. What is the ratio of boys to girls who went to the concert?

GCSE Quiz True

There are 500 people and 240 boys.

500-240=260. There are 260 girls.

The order of the ratio is boys to girls.

Boys : Girls

2. A musical requires 200 costumes. 140 costumes are for the background dancers. The rest are for the lead roles. Write the ratio of the costumes for lead roles to background dancers in the simplest form.

There are 200 costumes. 140 costumes are for background dances.

200-140=60 lead role costumes

The ratio order of the ratio is lead roles to background dancers

Lead roles : Background dancers

\hspace{1cm} 60 : 140

The greatest common factor of 60 and 140 is 20\text{:}

Ratio Image 12 US

3. A shop is selling the same pencils in two different packs.

Which statement correctly compares the packs?

Pack \textbf{A}\text{:} \; 5 pens cost \$ 6.20

Pack \textbf{B}\text{:} \; 4 pens cost \$ 4.88

Pack A is \$ 1.32 cheaper per pencil than Pack B.

Pack B is \$ 1.32 cheaper per pencil than Pack A.

Pack A is \$ 0.02 cheaper per pencil than Pack B.

Pack B is \$ 0.02 cheaper per pencil than Pack A.

Offer A\text{:} \; 5 pencils cost \$ 6.20 → 5 : \$ 6.20

Ratio Image 13 US

Each pencil in Pack A costs \$ 1.24.

Offer B\text{:} \; 4 pencils for \$ 4.88 → 4 : \$4.88

Ratio Image 14 US

Each pencil in Pack B costs \$ 1.22.

\$ 1.24-\$ 1.22=\$ 0.02.

Offer B costs \$ 0.02 cheaper than Offer A.

4. The fraction of bananas in a bowl is \cfrac{13}{20}. Calculate the ratio of bananas to other pieces of fruit in the bowl.

The total number of pieces of fruit is 20. The number of bananas is 13.

As a bar model, this looks like

Ratio Image 15 US

The number of other pieces of fruit is therefore 7 (this is calculated by 20-13=7 or counting the number of red bars above).

The ratio of bananas to other pieces of fruit is therefore 13 : 7.

5. Given the exchange rate between US dollars (USD) and New Zealand dollars (NZD) is \$ 1 \; USD=\$ 1.63 \; NZD, convert \$ 50 \; USD to New Zealand dollars (NZD). Round to the nearest cent.

\$ 50 \, USD=\$ \rule{0.5cm}{0.15mm} \, NZD

Since each US dollar is equal to \$ 1.63 \, NZD, multiply the USD by 1.63 to find the number of \$ \, (NZD).

Ratio Image 16 US

\$ 50 \, USD=\$ 81.50 \, NZD

6. A soap is made by combining lavender soap with lemon soap. Each bar of soap weighs 330 \, g. If the ratio of lavender to lemon is 4 : 7,   how many grams of lemon soap are in each bar?

As there are 7+4=11   shares within the ratio

Ratio Image 17 US

330 \div 11=30 \, g   per share

Ratio Image 18 US

The amount of Lemon in the soap is equal to 7 \times 30=210 \, g

Ratio Image 19 US

While the term ratio is used in a variety of ways in the real world, the definition of ratio in math is the comparison of two or more values that have a constant relationship. Some examples of ratios are “ 2 dogs to 5 cats” or “ 24 miles per hour.”

A rate is a special type of ratio that compares different units. They are not synonyms, since not all ratios are rates. However, all rates are ratios, so they can be called by either name.

Ratio understanding is expanded to include more complex comparisons that involve exponents, variables and/or polynomials. This extends to include ratio relationships in proportions and linear equations. As students progress in their learning, they will become comfortable graphing, creating tables and equations that represent ratio relationships.

The next lessons are

  • Converting fractions, decimals and percentages

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Sharing between a Ratio

Example 1: Abbie and Ben share £120 in the ratio 2:1 Work out how much each of them get.

The first step is to work out how many equal parts there are. The ratio is 2:1 so there are 3 (2 + 1) equal parts

We now need to work out how much each of the parts is worth We divide the £120 between the 3 parts £120 ÷ 3 = £40 Each part is worth £40

Now we can work out how much Abbie and Ben get Abbie has 2 parts so she gets £80 (2 × £40) Ben has one part which is worth £40

You may find it useful to draw a diagram for ratio questions

Abbie has 2 parts and Ben has 1 part, we could represent this as 2 boxes for Abbie and 1 box for Ben:

problem solving with ratio

Each box must have the same amount in it and the total in all 3 boxes must be £120. We share £120 out evenly between the boxes (£120 ÷ 3 = £40)

problem solving with ratio

We can see that Abbie gets £80 (£40 + £40) and Ben gets £40

Example 2: A, B and C share £240 in the ratio 4:3:1 Work out how much each of them get.

problem solving with ratio

4 + 3 + 1 = 8 There are 8 equal parts

£240 ÷ 8 = £30 Each part is worth £30

problem solving with ratio

A gets 4 × £30 = £120 B gets 3 × £30 = £90 C gets 1 × £30 = £30

Example 3: A and B share some money in the ratio 5:2 A gets £40 Work out how much B gets.

In this example we have not been given the total amount. We have been given the amount that A gets

problem solving with ratio

A has £40 and that is 5 parts

Each part much be equal so each part is worth £40 ÷ 5 £40 ÷ 5 = £8

problem solving with ratio

Each part is worth £8 and B has two parts £8 × 2 = £16

problem solving with ratio

Example 4: C and D share some money in the ratio 3:5 The difference between the amount C gets and the amount D gets is £18 Work out how much each of them get.

In this example we have been given the difference between the amounts of money C and D get.

problem solving with ratio

The difference between 3 parts and 5 parts is 2 parts. (5 − 3 = 2) 2 parts must be worth £18 £18 ÷ 2 = £9

problem solving with ratio

Each part is worth £9

problem solving with ratio

C gets 3 × £9 = £27 D gets 5 × £9 = £45

problem solving with ratio

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→ → Ratios

Find here an unlimited supply of worksheets with simple word problems involving ratios, meant for 6th-8th grade math. In , the problems ask for a specific ratio (such as, " "). In , the problems are the same but the ratios are supposed to be simplified.

contains varied word problems, similar to these:

Options include choosing the number of problems, the amount of workspace, font size, a border around each problem, and more. The worksheets can be generated as PDF or html files.


Each worksheet is randomly generated and thus unique. The and is placed on the second page of the file.

You can generate the worksheets — both are easy to print. To get the PDF worksheet, simply push the button titled " " or " ". To get the worksheet in html format, push the button " " or " ". This has the advantage that you can save the worksheet directly from your browser (choose File → Save) and then in Word or other word processing program.

Sometimes the generated worksheet is not exactly what you want. Just try again! To get a different worksheet using the same options:



What is the ratio given in the word problem? (grade 6)

   
 

What is the ratio given in the word problem? (with harder numbers; grade 6)

   
 

Solve ratio word problems (grade 7)
 

   
 

Solve ratio word problems
(more workspace; grade 7)

   
 

Use the generator to make customized ratio worksheets. Experiment with the options to see what their effect is.

 
(These determine the number of problems)


(only for levels 1 & 2):
      Range from
Page orientation:
    Font Size: 


Workspace: lines below each problem
Additional title & instructions  (HTML allowed)


Primary Grade Challenge Math cover

Primary Grade Challenge Math by Edward Zaccaro

A good book on problem solving with very varied word problems and strategies on how to solve problems. Includes chapters on: Sequences, Problem-solving, Money, Percents, Algebraic Thinking, Negative Numbers, Logic, Ratios, Probability, Measurements, Fractions, Division. Each chapter’s questions are broken down into four levels: easy, somewhat challenging, challenging, and very challenging.

Ratio Problem Solving ( Edexcel GCSE Maths: Foundation )

Revision note.

Naomi C

Ratio Problem Solving

What type of ratio problems could i be asked to solve.

  • Writing ratios
  • The link between ratios and fractions 
  • Equivalent ratios
  • Simplifying ratios
  • Sharing an amount in a given ratio 
  • E.g.,  Kerry is given $30 more than Kacey who is given $50
  • E.g.,  Kerry and Kacey are sharing money in the ratio 8 : 5, Kacey gets $50
  • E.g.,  Kerry and Kacey are sharing money in the ratio 8 : 5 whilst Kacey is also sharing money with Kylie in the ratio 1 : 2

How do I solve a ratio problem when given the difference between two parts?

  • Find the difference in the number of parts between the two quantities in the ratio
  • Compare the difference in the number of parts with the difference between the actual numbers  
  • Simplify to find out the value of one part
  • Multiply the value of one part by the number of parts for each quantity in the ratio 
  • Multiply the value of one part by the total number of parts to find the total amount

Given one quantity of a ratio, how can I find the other quantity?

  • Compare the given quantity  with the relevant number of parts in the ratio
  • Simplify to find the value of one part
  • Multiply the value of one part by the number of parts in the remaining quantity in the ratio

How do I combine two ratios to make a three-part ratio?

  • Identify the link between the two different ratios 
  • Find equivalent ratios  for both original ratios, where the value of the link is the same
  • Join the two, two-part ratios into a three-part ratio

Worked example

The ratio of cabbage leaves eaten by two rabbits, Alfred and Bob, is 8 : 4 respectively. It is known that Alfred eats 12 more cabbage leaves than Bob for a particular period of time. Find the total number of cabbage leaves eaten by the rabbits and the number that each rabbit eats individually.

The difference in the number of parts is

8 - 4 = 4 parts

This means that

4 parts = 12 cabbage leaves

Dividing both by 4

1 part = 3 cabbage leaves

Find the total number of parts

8 + 4 = 12 parts

Find the total number of cabbage leaves

12  × 3 = 36

36 cabbage leaves in total

Find the number eaten by Alfred

24 cabbage leaves

Find the number eaten by Bob

12 cabbage leaves

A particular shade of pink paint is made using 3 parts red paint, to two parts white paint.

Mark already has 36 litres of red paint, but no white paint. Calculate the volume of white paint that Mark needs to purchase in order to use all of his red paint, and calculate the total amount of pink paint this will produce.

The ratio of red to white is

Mark already has 36 litres of red, so

36 litres = 3 parts

Divide both sides by 3.

12 litres = 1 part

The ratio was 3 : 2 Find the volume of white paint, 2 parts

2  × 12 = 24

24 litres of white paint

In total there are 5 parts, so the total volume of paint will be

5 × 12 = 60

60 litres in total

In Jamie’s sock drawer the ratio of black socks to striped socks is 5 : 2 respectively. The ratio of striped socks to white socks in the drawer is 6 : 7 respectively.

Calculate the percentage of socks in the drawer that are black.

Write down the ratios

B : S = 5 : 2 S : W = 6 : 7

S features in both ratios, so we can use it as a link Multiply the B : S ratio by 3 to find an equivalent ratio Both ratios are now comparing to 6 striped socks

B : S = 15 : 6 S : W = 6 : 7

Link them together

B : S : W = 15 : 6 : 7

15 + 6 + 7 = 28

This means 15 out of 28 socks are black Find 15 out of 28 as a decimal by completing the division

Convert to a percentage Multiply by 100 and round to 3 significant figures

53.6 % of the socks are black

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Author: Naomi C

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

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Solving Ratio Problems

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  • We add the parts of the ratio to find the total number of parts.
  • There are 2 + 3 = 5 parts in the ratio in total.
  • To find the value of one part we divide the total amount by the total number of parts.
  • 50 ÷ 5 = 10.
  • We multiply the ratio by the value of each part.
  • 2:3 multiplied by 10 gives us 20:30.
  • The 50 counters are shared into 20 counters to 30 counters.

videolesson.JPG

  • 2 + 3 = 5 and so there are 5 parts in the ratio in total.
  • We divide by this total number of parts to find the value of each part.
  • We multiply the original ratio by the value of each part.
  • We have 20:30.

videolesson.JPG

  • Sharing in a Ratio: Part 1

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Ratio Problems: Worksheets and Answers

ratio problems worksheet pdf

How to Solve Ratio Problems

Share £50 in the ratio 2:3

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A ratio compares values .

A ratio says how much of one thing there is compared to another thing.

Ratios can be shown in different ways:

Use the ":" to separate the values:   3 : 1
     
Or we can use the word "to":   3 to 1
     
Or write it like a fraction:  

A ratio can be scaled up:

Try it Yourself

Using ratios.

The trick with ratios is to always multiply or divide the numbers by the same value .

is the same as ×2 ×2

 

Example: A Recipe for pancakes uses 3 cups of flour and 2 cups of milk.

So the ratio of flour to milk is 3 : 2

To make pancakes for a LOT of people we might need 4 times the quantity, so we multiply the numbers by 4:

3 ×4 : 2 ×4 = 12 : 8

In other words, 12 cups of flour and 8 cups of milk .

The ratio is still the same, so the pancakes should be just as yummy.

"Part-to-Part" and "Part-to-Whole" Ratios

The examples so far have been "part-to-part" (comparing one part to another part).

But a ratio can also show a part compared to the whole lot .

Example: There are 5 pups, 2 are boys, and 3 are girls

Part-to-Part:

The ratio of boys to girls is 2:3 or 2 / 3

The ratio of girls to boys is 3:2 or 3 / 2

Part-to-Whole:

The ratio of boys to all pups is 2:5 or 2 / 5

The ratio of girls to all pups is 3:5 or 3 / 5

Try It Yourself

We can use ratios to scale drawings up or down (by multiplying or dividing).

The height to width ratio of the Indian Flag is

So for every (inches, meters, whatever) of height
there should be of width.

If we made the flag 20 inches high, it should be 30 inches wide.

If we made the flag 40 cm high, it should be 60 cm wide (which is still in the ratio 2:3)

Example: To draw a horse at 1/10th normal size, multiply all sizes by 1/10th

This horse in real life is 1500 mm high and 2000 mm long, so the ratio of its height to length is

1500 : 2000

What is that ratio when we draw it at 1/10th normal size?

1500 : 2000   = 1500 : 2000
    =

We can make any reduction/enlargement we want that way.

Allie measured her foot and it was 21cm long, and then she measured her Mother's foot, and it was 24cm long.

"I must have big feet, my foot is nearly as long as my Mom's!"

But then she thought to measure heights, and found she is 133cm tall, and her Mom is 152cm tall.

In a table this is:

  Allie Mom
Length of Foot: 21cm 24cm
Height: 133cm 152cm

The "foot-to-height" ratio in fraction style is:

Allie:   Mom:

We can simplify those fractions like this:

And we get this (please check that the calcs are correct):

"Oh!" she said, "the Ratios are the same".

"So my foot is only as big as it should be for my height, and is not really too big."

You can practice your ratio skills by Making Some Chocolate Crispies

  • Math Article
  • Ratios And Proportion

Ratios and Proportion

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Ratio and Proportion are explained majorly based on fractions. When a fraction is represented in the form of a:b, then it is a ratio whereas a proportion states that two ratios are equal. Here, a and b are any two integers.  The ratio and proportion are the two important concepts, and it is the foundation to understand the various concepts in mathematics as well as in science.

problem solving with ratio

In our daily life, we use the concept of ratio and proportion such as in business while dealing with money or while cooking any dish, etc. Sometimes, students get confused with the concept of ratio and proportion. In this article, the students get a clear vision of these two concepts with more solved examples and problems.

For example, ⅘ is a ratio and the proportion statement is 20/25 = ⅘. If we solve this proportional statement, we get:

20 x 5 = 25 x 4

Check: Ratio and Proportion PDF

Therefore, the ratio defines the relationship between two quantities such as a:b, where b is not equal to 0. Example: The ratio of 2 to 4 is represented as 2:4 = 1:2. And the statement is said to be in proportion here. The application of proportion can be seen in direct proportion .

What is Ratio and Proportion in Maths?

The definition of ratio and proportion is described here in this section. Both concepts are an important part of Mathematics. In real life also, you may find a lot of examples such as the rate of speed (distance/time) or price (rupees/meter) of a material, etc, where the concept of the ratio is highlighted.

Proportion is an equation that defines that the two given ratios are equivalent to each other. For example, the time taken by train to cover 100km per hour is equal to the time taken by it to cover the distance of 500km for 5 hours. Such as 100km/hr = 500km/5hrs.

Ratios and Proportion

Let us now learn Maths ratio and proportion concept one by one.

Ratio Meaning

In certain situations, the comparison of two quantities by the method of division is very efficient. We can say that the comparison or simplified form of two quantities of the same kind is referred to as a ratio. This relation gives us how many times one quantity is equal to the other quantity. In simple words, the ratio is the number that can be used to express one quantity as a fraction of the other ones.

The two numbers in a ratio can only be compared when they have the same unit. We make use of ratios to compare two things. The sign used to denote a ratio is ‘:’.

A ratio can be written as a fraction, say 2/5. We happen to see various comparisons or say ratios in our daily life.

Hence, the ratio can be represented in three different forms, such as:

Key Points to Remember: 

  • The ratio should exist between the quantities of the same kind
  • While comparing two things, the units should be similar
  • There should be significant order of terms
  • The comparison of two ratios can be performed, if the ratios are equivalent like the fractions

Definition of Proportion

Proportion is an equation that defines that the two given ratios are equivalent to each other. In other words, the proportion states the equality of the two fractions or the ratios. In proportion, if two sets of given numbers are increasing or decreasing in the same ratio, then the ratios are said to be directly proportional to each other.

For example, the time taken by train to cover 100km per hour is equal to the time taken by it to cover the distance of 500km for 5 hours. Such as 100km/hr = 500km/5hrs.

Ratio and proportions are said to be faces of the same coin. When two ratios are equal in value, then they are said to be in proportion . In simple words, it compares two ratios. Proportions are denoted by the symbol  ‘::’ or ‘=’.

The proportion can be classified into the following categories, such as:

Direct Proportion

Inverse proportion, continued proportion.

Now, let us discuss all these methods in brief:

The direct proportion describes the relationship between two quantities, in which the increases in one quantity, there is an increase in the other quantity also. Similarly, if one quantity decreases, the other quantity also decreases. Hence, if “a” and “b” are two quantities, then the direction proportion is written as a∝b.

The inverse proportion describes the relationship between two quantities in which an increase in one quantity leads to a decrease in the other quantity. Similarly, if there is a decrease in one quantity, there is an increase in the other quantity. Therefore, the inverse proportion of two quantities, say “a” and “b” is represented by a∝(1/b).

Consider two ratios to be a: b and c: d .

Then in order to find the continued proportion for the two given ratio terms, we convert the means to a single term/number. This would, in general, be the LCM of means.

For the given ratio, the LCM of b & c will be bc.

Thus, multiplying the first ratio by c and the second ratio by b, we have

First ratio- ca:bc

Second ratio- bc: bd

Thus, the continued proportion can be written in the form of ca: bc: bd

Ratio and Proportion Formula

Now, let us learn the Maths ratio and proportion formulas here.

Ratio Formula

Assume that, we have two quantities (or two numbers or two entities) and we have to find the ratio of these two, then the formula for ratio is defined as;

where a and b could be any two quantities .

Here, “a” is called the first term or antecedent , and “b” is called the second term or consequent .

Example: In ratio 4:9, is represented by 4/9, where 4 is antecedent and 9 is consequent.

If we multiply and divide each term of ratio by the same number (non-zero), it doesn’t affect the ratio.

Example: 4:9 = 8:18 = 12:27

Also, read:    Ratio Formula

Proportion Formula

Now, let us assume that, in proportion, the two ratios are a:b & c:d. The two terms ‘b’ and ‘c’ are called  ‘means or mean term,’ whereas the terms ‘a’ and ‘d’ are known as ‘ extremes or extreme terms.’

 

Example:  Let us consider one more example of a number of students in a classroom. Our first ratio of the number of girls to boys is 3:5 and that of the other is 4:8, then the proportion can be written as:

3 : 5 ::  4 : 8 or 3/5 = 4/8

Here, 3 & 8 are the extremes, while 5 & 4 are the means.

Note: The ratio value does not affect when the same non-zero number is multiplied or divided on each term.

Important Properties of Proportion

The following are the important properties of proportion:

  • Addendo – If a : b = c : d, then a + c : b + d
  • Subtrahendo – If a : b = c : d, then a – c : b – d
  • Dividendo – If a : b = c : d, then a – b : b = c – d : d
  • Componendo – If a : b = c : d, then a + b : b = c+d : d
  • Alternendo – If a : b = c : d, then a : c = b: d
  • Invertendo – If a : b = c : d, then b : a = d : c
  • Componendo and dividendo – If a : b = c : d, then a + b : a – b = c + d : c – d

Difference Between Ratio and Proportion

To understand the concept of ratio and proportion, go through the difference between ratio and proportion given here.

S.No Ratio Proportion
1 The ratio is used to compare the size of two things with the same unit The proportion is used to express the relation of two ratios
2 It is expressed using a colon (:), slash (/) It is expressed using the double colon (::) or equal to the symbol (=)
3 It is an expression It is an equation
4 Keyword to identify ratio in a problem is “to every” Keyword to identify proportion in a problem is “out of”

Fourth, Third and Mean Proportional

If a : b = c : d, then:

  • d is called the fourth proportional to a, b, c.
  • c is called the third proportion to a and b.
  • Mean proportional between a and b is √(ab).

Comparison of Ratios

If (a:b)>(c:d) = (a/b>c/d)

The compounded ratio of the ratios: (a : b), (c : d), (e : f) is (ace : bdf).

Duplicate Ratios

If a:b is a ratio, then:

  • a 2 :b 2  is a duplicate ratio
  • √a:√b is the sub-duplicate ratio
  • a 3 :b 3 is a triplicate ratio

Ratio and Proportion Tricks

Let us learn here some rules and tricks to solve problems based on ratio and proportion topics.

  • If u/v = x/y, then uy = vx
  • If u/v = x/y, then u/x = v/y
  • If u/v = x/y, then v/u = y/x
  • If u/v = x/y, then (u+v)/v = (x+y)/y
  • If u/v = x/y, then (u-v)/v = (x-y)/y
  • If u/v = x/y, then (u+v)/ (u-v) = (x+y)/(x-y), which is known as componendo -Dividendo Rule
  • If a/(b+c) = b/(c+a) = c/(a+b) and a+b+ c ≠0, then a =b = c

Ratio and Proportion Summary

  • Ratio defines the relationship between the quantities of two or more objects. It is used to compare the quantities of the same kind.
  • If two or more ratios are equal, then it is said to be in proportion.
  • The proportion can be represented in two different ways. Either it can be represented using an equal sign or by using a colon symbol. (i.e) a:b = c:d or a:b :: c:d
  • If we multiply or divide each term of the ratio by the same number, it does not affect the ratio.
  • For any three quantities, the quantities are said to be in continued proportion, if the ratio between the first and second quantity is equal to the ratio between the second and third quantity.
  • For any four quantities, they are said to be in continued proportion, if the ratio between the first and second quantities is equal to the ratio between the third and fourth quantities

Ratio And Proportion Examples

Example 1: 

Are the ratios 4:5 and 8:10 said to be in Proportion?

4:5= 4/5 = 0.8 and 8: 10= 8/10= 0.8

Since both the ratios are equal, they are said to be in proportion.

Are the two ratios 8:10 and 7:10 in proportion?

8:10= 8/10= 0.8 and 7:10= 7/10= 0.7

Since both the ratios are not equal, they are not in proportion.

Example 3: 

Given ratio are-

Find a: b: c.

Multiplying the first ratio by 5, second by 3 and third by 6, we have

a:b = 10: 15

b:c = 15 : 6

c:d = 6 : 24

In the ratio’s above, all the mean terms are equal, thus

a:b:c:d = 10:15:6:24

Check whether the following statements are true or false.

a] 12 : 18 = 28 : 56

b] 25 people : 130 people = 15kg : 78kg

The given statement is false.

12 : 18 = 12 / 18 = 2 / 3 = 2 : 3

28 : 56 = 28 / 56 = 1 / 2 = 1 : 2

They are unequal.

b] 25 persons : 130 persons = 15kg : 78kg

The given statement is true.

25 people : 130 people = 5: 26

15kg : 78kg = 5: 26

They are equal.

The earnings of Rohan is 12000 rupees every month and Anish is 191520 per year. If the monthly expenses of every person are around 9960 rupees. Find the ratio of the savings.

Savings of Rohan per month = Rs (12000-9960) = Rs. 2040

Yearly income of Anish = Rs. 191520

Hence, the monthly income of Anish = Rs. 191520/12 = Rs. 15960.

So, the savings of Anish per month = Rs (15960 – 9960) = Rs. 6000

Thus, the ratio of savings of Rohan and Anish is Rs. 2040: Rs.6000 = 17: 50.

Twenty tons of iron is Rs. 600000 (six lakhs). What is the cost of 560 kilograms of iron?

1 ton = 1000 kg 20 tons = 20000 kg The cost of 20000 kg iron = Rs. 600000 The cost of 1 kg iron = Rs{600000}/ {20000} = Rs. 30 The cost of 560 kg iron = Rs 30 × 560 = Rs 16800

The dimensions of the rectangular field are given. The length and breadth of the rectangular field are 50 meters and 15 meters. What is the ratio of the length and breadth of the field?

Length of the rectangular field = 50 m

Breadth of the rectangular field = 15 m

Hence, the ratio of length to breadth = 50: 15

⇒ 50: 15 = 10: 3.

Thus, the ratio of length and breadth of the rectangular field is 10:3.

Obtain a ratio of 90 centimetres to 1.5 meters.

The given two quantities are not in the same units.

Convert them into the same units.

1.5 m = 1.5 × 100 = 150 cm

Hence, the required ratio is 90 cm: 150 cm

⇒ 90: 150 = 3: 5

Therefore, the ratio of 90 centimetres to 1.5 meters is 3: 5.

There exists 45 people in an office. Out of which female employees are 25 and the remaining are male employees. Find the ratio of

a] The count of females to males.

b] The count of males to females.

Count of females = 25

Total count of employees = 45

Count of males = 45 – 25 = 20

The ratio of the count of females to the count of males

The count of males to the count of females

Example 10:

Write two equivalent ratios of 6: 4.

Given Ratio : 6: 4, which is equal to 6/4.

Multiplying or dividing the same numbers on both numerator and denominator, we will get the equivalent ratio.

⇒(6×2)/(4×2) = 12/8 = 12: 8

⇒(6÷2)/(4÷2) = 3/2 = 3: 2

Therefore, the two equivalent ratios of 6: 4 are 3: 2 and 12: 8

Example 11 : 

Out of the total students in a class, if the number of boys is 5 and the number of girls is 3, then find the ratio between girls and boys.

The ratio between girls and boys can be written as 3:5 (Girls: Boys). The ratio can also be written in the form of factor like 3/5.

Example 12: 

Two numbers are in the ratio 2 : 3. If the sum of numbers is 60, find the numbers.

Given, 2/3 is the ratio of any two numbers.

Let the two numbers be 2x and 3x.

As per the given question, the sum of these two numbers = 60

So, 2x + 3x = 60

Hence, the two numbers are;

2x = 2 x 12 = 24

3x = 3 x 12 = 36

24 and 36 are the required numbers.

Maths ratio and proportion are used to solve many real-world problems. Register with BYJU’S – The Learning App and get solutions for many difficult questions in easy methodology and followed by the step-by-step procedure.

Frequently Asked Questions on Ratios and Proportion

What is the ratio give an example., what is a proportion give example, how to solve proportions with examples, what is the concept of ratios, what are the two different types of proportions.

The two different types of proportions are: Direct Proportion Inverse Proportion

Can we express ratio in terms of fractions?

Yes, we can express ratio in terms of fractions. For example, 3: 4 can be expressed as 3/4.

What is the formula for ratio and proportion?

The formula for ratio is: x:y ⇒ x/y, where x is the first term and y is the second term. The formula for proportion is: p: q :: r : s ⇒ p/q = r/s, Where p and r are the first term in the first and second ratio q and s are the second term and in the first and second ratio.

Find the means and extremes of the proportion 1: 2 :: 3: 4.

In the given proportion 1: 2 :: 3: 4, Means are 2 and 3 Extremes are 1 and 4.

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5.5: Ratios and Proportions

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A bar graph titled Facebook Dominates the Social Media Landscape displays monthly active users of selected social networks and messaging services. Numbers represent million. The x-axis ranges from 0 to 2000, in increments of 400.The following social media apps are displayed: Facebook (2,006), WhatsApp (1,300), Messenger (1,200), WeChat (938), Instagram (700), Qzone (632), Weibo (340), Twitter (328), Pinterest (175), Snapchat (166), Vkontakte (95).

Learning Objectives

After completing this section, you should be able to:

  • Construct ratios to express comparison of two quantities.
  • Use and apply proportional relationships to solve problems.
  • Determine and apply a constant of proportionality.
  • Use proportions to solve scaling problems.

Ratios and proportions are used in a wide variety of situations to make comparisons. For example, using the information from Figure 5.15, we can see that the number of Facebook users compared to the number of Twitter users is 2,006 M to 328 M. Note that the "M" stands for million, so 2,006 million is actually 2,006,000,000 and 328 million is 328,000,000. Similarly, the number of Qzone users compared to the number of Pinterest users is in a ratio of 632 million to 175 million. These types of comparisons are ratios.

Constructing Ratios to Express Comparison of Two Quantities

Note there are three different ways to write a ratio , which is a comparison of two numbers that can be written as: /**/(\$ 1 =0.82\,{€})/**/, how many dollars should you receive? Round to the nearest cent if necessary.

Example 5.31

Solving a proportion involving weights on different planets.

A person who weighs 170 pounds on Earth would weigh 64 pounds on Mars. How much would a typical racehorse (1,000 pounds) weigh on Mars? Round your answer to the nearest tenth.

Step 1: Set up the two ratios into a proportion. Notice the Earth weights are both in the numerator and the Mars weights are both in the denominator.

170 64 = 1,000 x 170 64 = 1,000 x

Step 2: Cross multiply, and then divide to solve.

170 x = 1,000 ( 64 ) 170 x = 64,000 170 x 170 = 64,000 170 x = 376.5 170 x = 1,000 ( 64 ) 170 x = 64,000 170 x 170 = 64,000 170 x = 376.5

So the 1,000-pound horse would weigh about 376.5 pounds on Mars.

Your Turn 5.31

Example 5.32, solving a proportion involving baking.

A cookie recipe needs /**/1{\text{ inch}} =/**/ how many miles). Then use that scale to determine the approximate lengths of the other borders of the state of Wyoming.

Example 5.38

Solving a scaling problem involving model cars.

Die-cast NASCAR model cars are said to be built on a scale of 1:24 when compared to the actual car. If a model car is 9 inches long, how long is a real NASCAR automobile? Write your answer in feet.

The scale tells us that 1 inch of the model car is equal to 24 inches (2 feet) on the real automobile. So set up the two ratios into a proportion. Notice that the model lengths are both in the numerator and the NASCAR automobile lengths are both in the denominator.

1 24 = 9 x 24 ( 9 ) = x 216 = x 1 24 = 9 x 24 ( 9 ) = x 216 = x

This amount (216) is in inches. To convert to feet, divide by 12, because there are 12 inches in a foot (this conversion from inches to feet is really another proportion!). The final answer is:

216 12 = 18 216 12 = 18

The NASCAR automobile is 18 feet long.

Your Turn 5.38

Check your understanding.

/**/16:12/**/ /**/12:16/**/ /**/4:3/**/
/**/16:12/**/ /**/12:16/**/ /**/16:28/**/ /**/28:12/**/ None of these
625 6,250 3,456 345.6 None of these

Section 5.4 Exercises

1 2 3 4
128 460 /**/b/**/ 541
$163.84 /**/a/**/ $277.76 /**/c/**/

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Multi-objective optimization for finding main design factors of a two-stage helical gearbox with second-stage double gear sets using the eamr method.

problem solving with ratio

1. Introduction

2. optimization problem, 2.1. calculation of gearbox mass, 2.2. calculation of gearbox efficiency, 2.3. objective functions and constrains, 2.3.1. objectives functions, 2.3.2. constrains, 3. methodology, 3.1. method to solve the multi-objective optimization, 3.2. method to solve mcdm problem:, 3.3. method to find the weight of criteria:, 4. single-objective optimization, 5. multi-objective optimization, 6. conclusions, author contributions, data availability statement, acknowledgments, conflicts of interest.

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Click here to enlarge figure

ParameterNomenclatureUnits
Allowable contact stress of stages i (i = 1 ÷ 2)AS Mpa
Allowable shear stress of shaft material [τ] MPa
Arc of approach on i stage -
Arc of recess on i stage -
Base circle radius of the pinion mm
Base circle radius of the gear mm
Center distance of stage 1a mm
Center distance of stage 2a mm
Coefficient of wheel face width of stage 1X -
Coefficient of wheel face width of stage 2X -
Coefficient of gear materialk Mpa
Contacting load ratio for pitting resistancek -
Diameter of shaft id mm
Efficiency of a helical gearboxη -
Efficiency of the i stage of the gearboxη -
Efficiency of a helical gear unitη -
Efficiency of a rolling bearing pairη -
Friction coefficientf-
Friction coefficient of bearingf -
Gearbox ratio (or total gearbox ratio)u
Gear ratio of stage 1u -
Gear ratio of stage 2u -
Gear width of stage 1b mm
Gear width of stage 2b mm
Gearbox massm kg
Gear massm kg
Shaft massm kg
Gearbox housing massm kg
Gear mass of stage 1m kg
Gear mass of stage 2m kg
Hydraulic moment of power lossesT Nm
ISO Viscosity Grade numberVG -
Length of shaft il mm
Load of bearing iFiN
Mass density of gearbox housing materials kg/m
Mass of shaft j (j = 1 ÷ 3)m kg
Mass density of shaft material kg/m
Outside radius of the pinion mm
Outside radius of the gear mm
Output torqueT Nmm
Pitch diameter of the pinion of stage 1d mm
Pitch diameter of the gear of stage 2d mm
Pitch diameter of the pinion of stage 2d mm
Pitch diameter of the gear of stage 2d mm
Power loss in the gearsPlgKw
Power loss in the bearingsPlbKw
Power loss in the sealsPlsKw
Power loss in the idle motionPzoKw
Pressure angleαrad.
Peripheral speed of bearingv m/s
Sliding velocity of gearvm/s
Total power loss in the gearboxPl-
Torque on the pinion of stage i (i = 1 ÷ 2)T Nmm
Volume coefficients of the pinione -
Volume coefficients of the geare -
Volume of gearbox housing V dm
Volumes of bottom housing AV dm
Volumes of bottom housing BV dm
Volumes of bottom housing BV dm
Weight density of gear materials kg/m
ParameterSymbolLower LimitUpper Limit
Gearbox ratio of first stageu 19
CWFW of stage 1X 0.250.4
CWFW of stage 2X 0.250.4
u u
Lower LimitUpper Limit
101.762.4
152.492.99
203.173.52
253.764.01
304.194.63
354.585.23
404.935.80
Trial.u X X m (kg)η (%)
14.290.250.25222.7496.04
24.290.250.29226.1895.97
34.290.250.33229.6095.92
44.290.250.36232.9895.86
54.290.250.40236.3295.79
64.290.290.25223.9595.45
254.290.400.40240.9193.04
264.310.250.25222.6996.02
274.310.250.29226.1395.97
514.340.250.25222.6596.00
524.340.250.29226.0895.95
534.340.250.33229.5095.88
764.360.250.25222.6095.98
774.360.250.29226.0495.93
784.360.250.33229.4595.86
1014.380.250.25222.5695.95
1024.380.250.29225.9995.91
1034.380.250.33229.4195.84
1234.380.400.33234.0993.01
1244.380.400.36237.4592.95
1254.380.400.40240.7792.88
Trial.n v G RiRank
m η m η m η
10.92461.00000.45170.51140.45170.51141.13223
20.93890.99930.45870.51110.45870.51111.114215
30.95310.99880.46560.51080.46560.51081.097029
40.96710.99810.47250.51050.47250.51051.080448
50.98090.99740.47930.51010.47930.51011.064475
60.92960.99390.45420.50830.45420.50831.11927
251.00000.96880.48860.49550.48860.49551.0141121
260.92440.99980.45160.51130.45160.51131.13221
270.93860.99930.45860.51110.45860.51111.114412
510.92420.99960.45150.51120.45150.51121.13224
520.93840.99910.45850.51100.45850.51101.114411
530.95260.99830.46540.51060.46540.51061.097027
760.92400.99940.45140.51110.45140.51111.13222
770.93830.99890.45840.51080.45840.51081.114414
780.95240.99810.46530.51050.46530.51051.097026
1010.92380.99910.45140.51100.45140.51101.13205
1020.93810.99860.45830.51070.45830.51071.114413
1030.95230.99790.46520.51040.46520.51041.097030
1230.97170.96850.47470.49530.47470.49531.0433100
1240.98560.96780.48160.49500.48160.49501.0279115
1250.99940.96710.48830.49460.48830.49461.0129125
No.u
10152025303540
u 2.042.743.363.854.314.765.16
X 0.250.250.250.250.250.250.25
X 0.250.250.250.250.250.250.25
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Share and Cite

Dinh, V.-T.; Tran, H.-D.; Vu, D.-B.; Vu, D.; Vu, N.-P.; Do, T.-T. Multi-Objective Optimization for Finding Main Design Factors of a Two-Stage Helical Gearbox with Second-Stage Double Gear Sets Using the EAMR Method. Symmetry 2024 , 16 , 783. https://doi.org/10.3390/sym16070783

Dinh V-T, Tran H-D, Vu D-B, Vu D, Vu N-P, Do T-T. Multi-Objective Optimization for Finding Main Design Factors of a Two-Stage Helical Gearbox with Second-Stage Double Gear Sets Using the EAMR Method. Symmetry . 2024; 16(7):783. https://doi.org/10.3390/sym16070783

Dinh, Van-Thanh, Huu-Danh Tran, Duc-Binh Vu, Duong Vu, Ngoc-Pi Vu, and Thi-Tam Do. 2024. "Multi-Objective Optimization for Finding Main Design Factors of a Two-Stage Helical Gearbox with Second-Stage Double Gear Sets Using the EAMR Method" Symmetry 16, no. 7: 783. https://doi.org/10.3390/sym16070783

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    Thinking Blocks Ratios - Learning Connections. Essential Skills. Problem Solving - model and solve word problems. Common Core Connection for Grades 6 and 7. Understand the concept of ratio and describe the relationship between two quantities. Use ratio and rate reasoning to solve real-world and mathematical problems.

  17. Ratios

    Using Ratios. The trick with ratios is to always multiply or divide the numbers by the same value. Example: A Recipe for pancakes uses 3 cups of flour and 2 cups of milk. So the ratio of flour to milk is 3 : 2. To make pancakes for a LOT of people we might need 4 times the quantity, so we multiply the numbers by 4: 3 ×4 : 2 ×4 = 12 : 8.

  18. Ratio and Proportion

    Examples. For example, ⅘ is a ratio and the proportion statement is 20/25 = ⅘. If we solve this proportional statement, we get: 20/25 = ⅘. 20 x 5 = 25 x 4. 100 = 100. Check: Ratio and Proportion PDF. Therefore, the ratio defines the relationship between two quantities such as a:b, where b is not equal to 0.

  19. 5.5: Ratios and Proportions

    Use proportions to solve scaling problems. Ratios and proportions are used in a wide variety of situations to make comparisons. For example, using the information from Figure 5.15, we can see that the number of Facebook users compared to the number of Twitter users is 2,006 M to 328 M. Note that the "M" stands for million, so 2,006 million is ...

  20. RATIO AND PROPORTION

    Learn how to solve problems involving ratio and proportion with Dr Austin Maths, a website that provides free and editable resources for maths teachers and students. You can also find topics such as equations, inequalities, graphs, calculus and statistics on the website.

  21. Solving ratio problems with tables (video)

    The ratio 3 to 5 or 3/5 is the same thing as 12 to 20, is the same thing as 24 to 40, is the same thing as 48 to 80. Let's make sure we got the right answer. Let's do a couple more of these. The following table shows equivalent fractions to 27/75. So then they wrote all of the different equivalent fractions.

  22. Level 6 Math

    Multiplication, division, fractions, and logic games that boost sixth grade math skills. Level 6 Math Games Game Spotlight: Dirt Bike Proportions Multiplayer Math Games Four Wheel Fracas. Jumping Aliens. Martian Hoverboards. Otter Rush. ... Logic and Problem Solving Games Icy Super Slide. Arcade Golf. Rabbit Samurai 2. Duck Life 4. Icy Purple ...

  23. Equivalent ratio word problems (practice)

    Equivalent ratio word problems. A fruit basket is filled with 8 bananas, 3 oranges, 5 apples, and 6 kiwis. Complete the ratio. Learn for free about math, art, computer programming, economics, physics, chemistry, biology, medicine, finance, history, and more. Khan Academy is a nonprofit with the mission of providing a free, world-class education ...

  24. Symmetry

    When optimizing a mechanical device, the symmetry principle provides important guidance. Minimum gearbox mass and maximum gearbox efficiency are two single objectives that need to be achieved when designing a gearbox, and they are not compatible. In order to address the multi-objective optimization (MOO) problem with the above single targets involved in building a two-stage helical gearbox ...

  25. Proportion word problems (practice)

    Proportion word problems. Sam used 6 loaves of elf bread on an 8 day hiking trip. He wants to know how many loaves of elf bread ( b) he should pack for a 12 day hiking trip if he eats the same amount of bread each day. How many loaves of elf bread should Sam pack for a 12 day trip? Learn for free about math, art, computer programming, economics ...

  26. Medium: Problem solving and data analysis

    This unit tackles the medium-difficulty problem solving and data analysis questions on the SAT Math test. Work through each skill, taking quizzes and the unit test to level up your mastery progress. ... Ratios, rates, and proportions: medium Get 3 of 4 questions to level up! Unit conversion: medium. Learn. Unit conversion | Lesson (Opens a modal)