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Approximation

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Making estimates

Rounding prices

Imagine that you are buying a t-shirt for £9.99, a pair of socks for £1.49 and a belt for £8.99 The cashier charges you £23.47. You feel that this is too much - but how do you know?

One way of finding out whether you have been over-charged is to estimate what the total amount should be. Round the different prices into easier numbers - £9.99 is approximately £10, £1.49 is approximately £1.50 and £8.99 is approximately £9 - and you can do the calculation quickly in your head.

£9.99 + £1.49 + £8.99 £10 + £1.50 + £9 = £20.50

This is almost £3 less than the cashier asked for, so obviously you have been over-charged.

Note: the symbol means 'approximately equal to'.

Examples

By rounding the actual values to more manageable numbers, you can estimate the answers to many problems:

£2.99 + £3.10 + 99p £3 + £3 + £1 = £7

29 × 9 30 × 10 = 300

61 ÷ 6 60 ÷ 6 = 10

Activity

Approximation activity

Round up, round up and try this activity!

Play

Elemental

Can you conquer the elements?

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