Edexcel IGCSE Maths

Revision Notes

1.10.1 Rounding & Estimation

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
  • GENERAL RULE:
    Round numbers to 1 significant figure

    • 7.8 ➝ 8
    • 18 ➝ 20
    • 3.65 × 10-4 ➝ 4 × 10-4
    • 1080 ➝ 1000
  • EXCEPTIONS:
    It can be more sensible (or easier) to round to something convenient

    • 16.2 ➝ 15
    • 9.1 ➝ 10
    • 1180 ➝ 1200

It wouldn’t usually make sense to round a number to zero

  • FRACTIONS get bigger when the top is bigger and/or the bottom is smaller and vice versa

Worked Example

Rounding & Estimation, IGCSE & GCSE Maths revision notes

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