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Succeed with maths: part 1

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1.1 Finding a percentage of a value

Suppose that residents in a town are asked for their views on the proposed development of a nearby wind farm. The local paper says that 450 people voted, with 54 per cent in favour of the proposal, 36 per cent against and 10 per cent undecided. How can you find out 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. There are two ways to work this out. You can either start by converting the percentage to a fraction, or alternatively to a decimal number.

• As a fraction: .
• As a decimal: 54 % = 54 ÷ 100 = 0.54.

Now remember that when ‘of’ is used in maths, it is usually an instruction to multiply.

Using the fraction conversion, write the calculation as:

So 243 people were in favour of the proposal.

So to calculate a percentage of a number, first convert the percentage to either a fraction or a decimal, and then multiply it by the given number. Have a go at this in the next activity.

Activity 2 Number of voters

Timing: Allow approximately 10 minutes

Find the number of people who were against the proposed wind farm, and then find the number of people who were undecided about the proposal. (Try this second calculation without using the calculator.)