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20% of a number. Three different methods to work out 20% of something.

Updated on January 02, 2013

Here I will show you 3 different ways that you can work out 20% of a number.

Method 1 (by converting 20% into a fraction)

20% means 20 out of 100. So if you write this is a fraction you get 20/100 which can be simplified to 1/5. So instead of finding 20% of your number you can work out 1/5 of your number – to do this just divide the number by 5.

For example, work out 20% of 65ml.

So all you need to do is work out 1/5 of 65ml:

65 ÷ 5 = 13ml

Method 2 (By converting 20% into a decimal)

Alternatively you can convert 20% into a decimal by dividing 20% by 100:

20% ÷ 100 = 0.2

Once this is done all you need to do is multiply your number by 0.2.

For example, work out 20% of 46 inches.

So all you need to do is multiply 46 by 0.2

46 × 0.2 = 9.2 inches.

Method 3 (By working out 10%)

Since 20% is double the size of 10%, you can work out 10% then double your answer.

Working out 10% is easy to do, as all you have to do is divide your number by 10.

For example, work out 20% of 7000 litres.

10% of 7000 = 7000 ÷ 10 = 700

So 20% of 7000 = 700 + 700 = 1400.

Let’s look at one last example using all of the 3 different methods.

Example

Work out 20% of 2400kg

Method 1 (by converting 20% into a fraction)

So this is the same as working out 1/5 of 2400:

2400 ÷ 5 = 480

Method 2 (By converting 20% into a decimal)

0.2 × 2400 = 480

Method 3 (By using 10%)

10% of 2400 = 2400 ÷ 10 = 240

So 20% of 2400 = 240 + 240 = 480

As you can see all 3 methods give you the same answer of 480.

It’s up to you which method to use. Method 3 is probably the easiest method to apply as you can easily do this method in your head without the need of a calculator or any formal written methods of working out.

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