Estimation in Arithmetical Calculations (F)

Approximating is all about making the calculation easier, by rounding each number to 1 significant figure. Very often, you will then be able to do it in your head. Things can get a little bit trickier when division is involved – ideally, you want both the numerator and denominator to have a common factor, so that one is a multiple of the other and it will cancel down.

Working out an approximate answer will give you an indication of the size of the answer (this is often called the ‘ball park figure’).

If your approximation tells you the answer is in the hundreds, but your proper calculation gives an answer smaller than 1, then you know you have gone wrong somewhere. Engineering disasters have resulted from errors in calculations, so it is important to get it right!

Look for everyday opportunities to practise your estimating skills – what’s the total of your shopping basket, how much change would you get from a £20 note, how many MP3 downloads can I get from a £5 voucher… the list is endless!