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Maths

Percentages

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'Percent' means 'out of 100'. If 90 per cent of the population owns a mobile phone, this means 90 out of every 100 people have one. The symbol '%' means per cent.

Finding percentages

A percentage is a fraction of 100.

30% (30 in each 100) as a fraction is 30/100

30% as a decimal is 0.3.

Often, in real life - and maths exams - you must find a percentage of a quantity. First, write the percentage as a fraction or a decimal, then multiply by the quantity.

Have a look at this question:

Question

Find 40% of £50.

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Answer

First, write 40% as a fraction: 40% = 40/100 = 4/10 = 2/5

Now multiply by the quantity:

2/5 × 50 = £20.

Practise converting percentages to fractions. Then try the questions below.

Question

Sarah is buying a pair of jeans. The original price was £75, but there is a discount of 30%. How much will the discount be?sale

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Answer

Discount = 30% of 75

= 30/100 × 75

= 0.3 × 75

= £22.50

Note that if the question asked for the discount price, you would subtract the discount from the original price : £75 - £22.50 = £52.50.

Sometimes both the percentage and amount of money will not be whole numbers.

Question

A car costs £9,999.90 before VAT (value added tax). Work out the cost of the VAT if it is charged at 20%.

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Answer

VAT = 20% of £9,999.90

= 20/100 × 9,999.90

= 1,999.98

Since the answer is a price, it must be rounded to two decimal places.

The answer is £1,999.98

Income Tax

People pay tax on the income they earn. The basic rate of income tax is 20% (as of 2011).

VAT

Value Added Tax is added to the cost of most things you buy. It is charged at 20% (as of 2011).

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