Science, Maths & Technology

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# 5.1 Calculating a percentage of an amount

Working out the percentage of an amount requires a similar method to finding the fraction of an amount. Take a look at the examples below to increase your confidence.

## Case study _unit2.5.1 Example: Finding 17% of 80

### Method

17% of 80 = of 80, so we do:

#### Extract _unit2.5.1

80 ÷ 100 × 17 = 13.6

## Case study _unit2.5.2 Example: Finding 24% of 60

### Method

24% of 60 = of 60, so we do:

#### Extract _unit2.5.2

60 ÷ 100 × 24 = 14.4

Just as with fractions, you will often need to be able to work out the price of an item after it has been increased or decreased by a given percentage. The process for this is the same as with fractions; you simply work out the percentage of the amount and then add it to, or subtract it from, the original amount.

## Activity _unit2.5.1 Activity 9: Percentages of amounts

1. You earn £500 per month. You get a 5% pay rise.

• a.How much does your pay increase by?

• b.How much do you now earn per month?

1.

• a.5% of £500 =  of £500 = 500 ÷ 100 × 5 = £25.

• b.£500 + £25 = £525 per month.

1. You buy a new car for £9,500. By the end of the year its value has decreased by 20%.

• a.How much has the value of the car decreased by?

• b.How much is the car worth now?

1.

• a.20% of £9500 = of £9500 = £9500 ÷ 100 × 20 = £1900. The car has decreased by £1900.

• b.The car is now worth: £9500 − £1900 = £7600.

1. You invest £800 in a building society account which offers fixed-rate interest at 4% per year.

• a.How much interest do you earn in one year?

• b.How much do you have in your account at the end of the year?