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You will often have to find a value when an amount increases or decreases by a percentage. There is more than one way of working it out.

Try this Math quiz about percentages and numbers to get you familiar with the methods.

1.

Bob, the local car dealer, is reducing all his cars by 15%. Find the reduced price of a Nissan which originally cost £690.

£580.60

£585.50

£586.50

£590.90

Another way is to use a multiplier. A 15% decrease is a mutliplier of 100 - 15 = 85%. 85% = 0.85 (just divide 85 by 100). £690 x 0.85 = £586.50

2.

To find the result of decreasing a number by 7% you multiply it by .......

0.9

0.93

1.07

1.7

Percentages are easily converted to decimals. Just divide by 100 (or move digits)

3.

Thomas earns £22,500 per year. He receives a pay rise of 4.4%. How much does he now earn?

£23,000

£23,400

£23,450

£23,490

4.

Harold owns a 14% stake in a company worth £250,000. How much is Harold's stake worth?

£35,000

£40,000

£45,000

£50,000

5.

The local soccer team are playing badly and the number of season tickets sold reduces by 17% from last year. If 3,700 tickets were sold last year, how many were sold this year?

3,000

3,071

3,091

3,099

6.

In a sale, all the prices are reduced by 20%. Find the sale price of a washing machine which originally cost £299.

£60

£100

£176.30

£239.20

One way is 20 / 100 x £299 = £59.80. Then subtract £59.80 from £299 to get £239.20

7.

Simon bought his computer for £230. A year later he sold it for 20% less than he paid for it. How much was it sold for?

£164

£184

£204

£224

8.

To find the result of increasing a number by 66% you multiply it by .......

1.16

1.6

1.66

34

Calculations are much easier if a multiplier is used

9.

A train's top speed is 140 mph. After a service, its top speed increases by 12%. What is the new top speed?

150 mph

156 mph

156.4 mph

156.8 mph

A 12% increase is a multiplier of 1.12. 1.12 x 140 = 156.8

10.

To find the result of increasing a number by 13% you multiply it by .......

1.13

1.3

1.31

87

If something is increased by x% then its original value will have to be multiplied by (1 + x) to find the new value. The 1 represents 100% and the x represents the percentage increase: in this case (1 + x) = (1 + 0.13) = 1.13. If there was a decrease of x%, then you would have to multiply the original value by (1 - x)