1.9 Using percentages
You will find it easier to carry out the following example and activity using a calculator.
You have plenty of options when it comes to what calculator to use and you may find it easier to use one that you are most familiar with. This may be a calculator on your mobile phone, the calculator on your PC, laptop or tablet, an online calculator, or a handheld calculator.
Finding a percentage of a number
Suppose that residents in a town are asked their views on a proposed development of a wind farm near the town. The local paper says that 450 people voted, with 54 per cent in favour of the proposal, 36 per cent against the proposal and 10 per cent saying that they were undecided. How many people were in favour of the proposal?
To find the number of people who were in favour, you need to find 54 per cent of 450. This is similar to Activity 2, so we can perform the following calculation: 
.
So, 243 people were in favour of the proposal.
Activity 3 Methods for finding percentages
Now it’s your turn. Find the number of people who were against the proposal. Then find the number of people who were undecided about the proposal. (Try this calculation without using the calculator.)
Answer
Since 36 per cent of the 450 people were against the proposal, you want to calculate 36 per cent of 450 to find the exact number. Here are the two methods on the calculator.
Percentage against: 
So, 162 people were against the proposal.
You know that 10 per cent of the 450 people were undecided, so you need to find 10 per cent of 450. You should be able to do this calculation without the calculator: 10 per cent is one-tenth, and one-tenth of 450 is 45. So, 45 people were undecided. The calculator should give you the same answer, but do watch for easy calculations that you can do in your head – it’s good practice!
As a check, the three numbers you have calculated should add up to 450. The number in favour was 243, the number against was 162 and the number undecided was 45, and these do add up to 450.