Edexcel IGCSE Maths复习笔记 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

转载自savemyexam