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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.

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

2.

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)

3.

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

4.

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

5.

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)

6.

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

7.

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

8.

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

9.

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

10.

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