Finding a percentage of an amount using a multiplier

Home learning focus

In this lesson, you will learn how to find percentages of amounts using decimal multipliers. You will need a calculator.

This lesson includes:

  • a learning summary
  • two activities

Created in partnership with Numerise.

Learn

Recap: Finding percentages of amounts by hand

You should have already learnt how to find percentages of amounts by hand (without a calculator), but here is a quick recap.

If you needed to find 15% of 400 by hand, then there are a couple of different methods you could use:

Method 1: Find 1% of 400 and then multiply by 15

To find 1% of a number, you divide by 100, so:

1% of 400

400 ÷ 100 = 4

1% of 400 = 4

15% is 15 lots of 1%, so:

15% of 400

15 × 4 = 60

15% of 400 = 60

Method 2: Add together 10% and 5% of 400

You can break 15% into smaller percentages, for example:

15% = 10% + 5%

To find 10% of a number, divide by 10, so:

10% of 400

400 ÷ 10 = 40

5% is half of 10%, so 5% of 400 is half of 40, which is 20

15% of 400 = 10% of 400 + 5% of 400

15% of 400 = 40 + 20

15% of 400 = 60

Finding percentages of amounts using a decimal multiplier

Sometimes Method 1 and Method 2 can be slow, or the percentage may be hard to break down into smaller chunks. In these cases, you can use decimals.

Remember, percentages can be written as decimals. Look at the diagram below.

For our 15% of 400 example above, 15% written as a decimal is 0.15

You can use the decimal equivalent of a percentage to help us find percentages of amounts - you just need to multiply the amount by the decimal.

So to find 15% of 400, you would multiply 0.15 by 400. You can use a calculator.

0.15 × 400 = 60

Example: Find 27% of 300

First, rewrite 27% as a decimal.

27 ÷ 100 = 0.27

27% = 0.27

Then, use a calculator to multiply the original amount by the decimal multiplier.

0.27 × 300 = 81

So, 27% of 300 is 81.

Example: Find 36.2% of 640

First, rewrite 36.2% as a decimal.

36.2 ÷ 100 = 0.362

36.2% = 0.362

Then, use a calculator to multiply the original amount by the decimal multiplier.

0.362 × 640 = 231.68

So, 36.2% of 640 is 231.68.

Example: Find 112% of 86

Here the percentage is greater than 100%, but you can still use the same method.

First, rewrite 112% as a decimal.

112 ÷ 100 = 1.12

112% = 1.12

Then, use a calculator to multiply the original amount by the decimal multiplier.

1.12 × 86 = 96.32

So, 112% of 86 is 96.32.

Practise

Activity 1

Worksheet: Decimal multipliers

Practise finding percentages of amounts using this worksheet from Numerise.

You can print it out or write your answers on a piece of paper.

You will need to use a calculator, but don’t forget to write down your workings!

Using a calculator to find percentages of amounts

Activity 2

Worksheet: Finding the percentage of an amount using a multiplier

Have a go at this worksheet from Beyond where you have to find the percentage of amounts using a multiplier. You can print it out or write your answers on a piece of paper.

Finding the percentage of an amount using a multiplier

Finished? Click here for the answer sheet.

There's more to learn

KS3 Maths
The BBC Bitesize 14 day sort-your-life-out challenge
11 - 14 Maths
Holly Smale: My top tips for dealing with loneliness
video
Simon Singh's Numbers