How_To_Be_Good_At_Math

NUMBERS • CALCULATING PERCENTAGES 67

10% of 800

A percentage is

just another way of

writing a fraction.

Divide the total

amount by 100

300 ÷ 100 = 3

3 × 30 = 90

First, we need to find 1% of 300,

so we divide the 300 by 100.

Finding a percentage of a number

We can also use percentages to divide a number into parts. There’s

more than one way to do this, but one method is to start by finding 1%.

Next, we multiply the answer by

the percentage we need to find.

This gives us the answer:

30% of 300 is 90.

The 10% method

In the example above, we began by finding 1% of the

total. Sometimes, we can get to the answer more quickly

by first finding 10%. This is called the 10% method.

30% of 300 = 90

30% of 300 =?

6 × 35 = 210

350 ÷ 10 = 35

65% of £350 =?

We need to find 10% of £350,

so we divide the amount

by 10. This gives us 35.

In this example, we need

to work out 65% of £350.

We know that 10% is 35, so 60%

will be 6 groups of 35.

We’ve found 60% of 350. Now we just

need another 5% to get 65%. To work

out 5%, we simply halve the 10% amount.

Now add 60% and 5% to find

65%. So, 65% of £350 is £227.50.

210 + 17.50 = £227.50

35 ÷ 2 = 17.50

Let’s find 30% of 300.

10% of 550

10% of 200

10% challenge

Time yourself and see

how quickly you can

work out the following

percentages:

Answers on page 319

TRY IT OUT

066-067_Percentage_as_a_number.indd 67 29/02/2016 14:10