# Percentages of quantities

**Calculating percentages using fractions**

The “per cent” of a number is also fraction out of 100. For example, what is 15% of 90?

- 15% of 90, means “15 hundredths of 90”

or

**Calculating percentages using decimals**

Percentages can be calculated using an equivalent decimal operator.

4% of 9 = 0.04 × 9

= 4 × 9 ÷ 100

= 36 ÷ 100

= 0.36

Point to note: e

- Each step should be calculated mentally.

**Estimating percentages**

More difficult percentages can be found using a calculator. However, it is always sensible to make an estimate when using a calculator.

**Using a calculator**

There are a few ways to work out a percentage using a calculator, one method is by writing the percentage as a decimal. For example

What is 39% of £66?

39% = 0.39 (key the decimal in)

The answer is £25.74

Another way of work out a percentage is by converting the percentage to a fraction. For example,

What is 54% of £82?

54% = 54/100 = 54 ÷ 100

The answer is 44.28

We can also work out percentages by finding 1% first and then multiplying by the required percentage.

What is 37.5% of £59?

1% of £59 is £0.59 so, 37.5% of £59 is £0.59 × 37.5.

The answer is 22.125