Simplifying Ratios

Here we will learn about simplifying ratios, including how to simplify a ratio, how to write equivalent ratios and using simplifying ratio in real life problems.

There are also ratio worksheets and word problems based on Edexcel, AQA and OCR exam questions, along with further guidance on where to go next if you’re still stuck.

What is simplifying ratios?

Simplifying ratios is a way of using common factors to divide all the numbers in a ratio until they cannot be divided further.

A simplified ratio is equivalent to an non simplified ratio.

E.g.

Let’s look at 12 red counters and 16 blue counters.

If we organised them into a the two colours, we can get something that looks like this:

Each of the four rows contains 3 red counters and 4 blue counters. This allows us to express the ratio 12:16 as the ratio in the simplest form 3:4 .

We can simplify the ratio by finding the highest common factor or HCF (otherwise known as the greatest common factor or GCF) of each of the numbers in the ratio.

For the example above, the highest common factor would be 4 as we can divide 12 and 16 by 4 .

Bar modelling

We can use bar modelling to help us simplify ratios.

E.g.

Here are some circles.

Rearranging them into coloured bars, we can show the number of orange circles and the number of purple circles.

The number of orange circles is 4 , and the number of purple circles is 6 . This can be written as the ratio 4:6.

We can also rearrange these circles into another pattern:

Here, we still have the ratio of 4:6 but we have arranged them into two rows, each with the same proportion of circles.

Each row contains 2 orange circles, and three purple circles. This means that we can divide each side of the ratio by 2 , and still obtain the same ratio of orange to purple.

So by using bar modelling, we can simplify the ratio 4:6 to get 2:3.

How to simplify a ratio using the HCF

The fastest way to simplify a ratio is to use the highest common factor of the numbers in the ratio.

For example

If you are given a ratio of 64:80, to simplify it: first find the highest common factor which is 16; next divide each part of the ratio by the highest common factor 64 \div 16 : 80 \div 16 which gives you the answer 4:5

Ratio Simplifier

We can summarise simplifying ratios using this formula

The simplified ratio \mathrm{A}: \mathrm{B}=A \div H C F \text{ of }(A, B): B \div H C F \text{ of }(A, B)

For example.

Simplify 45:75

HCF of (45,75) = 15

\begin{aligned} 45: 75 & =45 \div 15: 75 \div 15 \\\\ & =3: 5 \end{aligned}

What is simplifying ratios?

How to simplify a ratio

In order to simplify a ratio:

1. Calculate the highest common factor of the parts of the ratio.
2. Divide each part of the ratio by the highest common factor.

How to simplify a ratio

Related lessons on ratio

Simplifying ratios is part of our series of lessons to support revision on ratio. You may find it helpful to start with the main ratio lesson for a summary of what to expect, or use the step by step guides below for further detail on individual topics. Other lessons in this series include:

• Ratio
• How to work out ratio 
• Ratio to fraction
• Dividing ratios
• Ratio problem solving
• Ratio scale
• Ratio to percentage

Simplifying ratios examples

Example 1: standard question

Simplify the ratio

1. Calculate the highest common factor of the parts of the ratio.

Listing the factors of 20 and 32 , we have:

2Divide each part of the ratio by the highest common factor.

Solution:

Example 2: three part ratio

Simplify the following ratio

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

Solution:

3:2:4

Example 3: ratio including decimals

Simplify the following ratio

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

Solution:

2:3

Example 4: fractions

Simplify the ratio

\frac{1}{2}:\frac{1}{6}

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

Solution:

3:1

Example 5: mixed numbers

Simplify the ratio

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

As we have two mixed numbers, we can convert them to improper fractions or decimals. We will look at converting the mixed numbers to decimals and then simplify the ratio.

Converting both of the mixed numbers to decimals we have 1\frac{1}{4}:2\frac{2}{5} s the same as 1.25:2.4

Multiplying both of these parts of the ratio by 100 will quickly remove the decimal so we can then simplify the ratio.

125:240

Calculating the highest common factor of 125 and 240 quickly by using prime factor trees, we get:

125 = 5\times 5\times 5

240 = 2\times 2\times 2\times 2\times 3\times 5

From this, we can show that the highest common factor of 125 and 240 is 5.

HCF(125,240) = 5

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

Solution:

25:48

Example 6: algebraic terms

Given that a, b, and c are all positive integers, simplify the ratio

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

Solution:

ab:c

Example 7: bar modelling

Use a bar model to simplify the ratio 8:10

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

Representing the ratio 8:10 as a bar model, we have

Where red represents 8 shares, and purple represents 10 shares.

HCF(8,10)=2

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

As the highest common factor is 2 , we divide the bar above into two bars containing the same amount of red shares, and purple shares.

Each bar is the ratio 4:5.

Solution:

4:5

Common misconceptions

• Not fully simplified

A common error is that the ratio is not cancelled to its simplest form due to not using the highest common factor,

E.g.

Simplify the ratio 12:18.

We can simplify by dividing parts of the ratio by dividing both numbers by 2 , leaving the ratio 6:9 .

This is not the final answer as it can be simplified further by dividing by 3 to get the ratio 2:3.

• Solution not written in the correct order

A common error is to change the order of the ratio. It is important that the order of the numbers in the ratio remains the same while simplifying.

• Not simplifying all parts of the ratio

When simplifying a ratio with more than two parts, a common misconception is to not simplify all of the parts of the ratio. 

E.g.

“Simplify the ratio 12:6:15 ” could be incorrectly written as 2:6:3 as the middle part is not cancelled down.

• Incorrect division

Some numbers are more tricky to divide than others, especially when calculating it mentally.

Common incorrect calculations include 15\div 5=5, 32\times 7=4, and 24\div 8=4

• Addition and subtraction?

We cannot use addition and subtraction to simplify a ratio, we can only use multiplication and division.

Let’s look at why using a visual representation:

Below are 15 rectangles (r) and 5 stars (s) .

If we were to express the number of stars and rectangles as a ratio, we would write the ratio 5:15 . Remember that the order is important and so we have written the number of stars first and the number of rectangles second (s:r) .

Dividing the number of rectangles by the number of stars we get \frac{r}{s}=3 .

Here the number 3 is known as the constant of proportionality (Step-by-step guide: Direct proportion).

Now if we were to subtract 1 from each of the stars and the rectangles above and divide the quantities again the answer should be 3 if the ratio was equivalent.

Subtracting 1 from each we now have 4 stars (S) and 14 rectangles (R) . I \frac{R}{S}=\frac{14}{4}=3.5 .

As this is not 3 the ratios are not equivalent.

• Ratios and decimals

Simplified ratios should not include decimals.

E.g.

If we want to simplify the ratio 9:12 , we need to divide each quantity in the ratio by a common factor. 

Here we have simplified by a common factor of 3 , and then simplified again by dividing these new numbers by 4 .

When simplifying a ratio, your solution must contain whole numbers (integers)

So the correct simplified ratio is:

The next lessons are

• Proportion
• Compound measures
• Best buy maths

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