Estimating calculations

Explore updated revision resources for GCSE Maths: How to estimate calculations, with step-by-step slideshows, quizzes, practice exam questions, and more!

Sometimes it is a good idea to estimate a calculation rather than work it out exactly, if you don’t need to know the exact value. In this situation, round the numbers in the question before performing the calculation. Usually, numbers are rounded to one significant figure. The 'approximately equal to' sign, ≈, is used to show that values have been rounded.

Examples

Estimate \(23 \times 67\).

Rounding to 1 significant figure gives: \(20 \times 70 = 1,400\)

Therefore: \(23 \times 67 \approx 1,400\)

Estimate: \(\frac{423 - 98}{16.4}\)

Rounding to 1 significant figure gives: \(\frac{400 - 100}{20} = \frac{300}{20} = \frac{30}{2} = 15\)

Therefore: \(\frac{423 - 98}{16.4} \approx 15\)

Question

Estimate \((58.4 \div 2.79) - 9.8\).

Question

Estimate \(\frac{68.7 - 9.9}{2.77}\).

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Approximation - OCREstimating calculations