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