Revision Notes

Why use estimation?

We ESTIMATE to find approximations for difficult sums or to check our answers are about the right size (right order of magnitude).

How to estimate

We ROUND numbers to something sensible before CALCULATING.

  1. GENERAL RULE:
    Round numbers to 1 significant figure 

    • 7.88
    • 1820
    • 3.65 × 10-44 × 10-4
    • 10801000
  2. EXCEPTIONS:
    It can be more sensible (or easier) to round to something convenient

    • 16.215
    • 9.110
    • 11801200
    • It wouldn’t usually make sense to round a number to zero
  3. FRACTIONS get bigger when the top is bigger and/or the bottom is smaller and vice versa

Example

Rounding & Estimation, IGCSE & GCSE Maths revision notes

Question

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