MEPX
Chapter 1 of 11All chapters
  1. 1Why bother
  2. 2Splitting numbers
  3. 3Rounding and compensating
  4. 4Doubling and halving
  5. 5Shortcuts worth knowing
  6. 6Percentages
  7. 7Fractions and decimals
  8. 8Squares and roots
  9. 9Division
  10. 10Estimation and checks
  11. 11Building speed

Chapter 1 of 11

Why bother

The point is judgement, not showing off.

Catching wrong answers

The value of mental arithmetic is noticing when a number on a screen is impossible. If you know roughly what the answer should be, a misplaced decimal point stands out immediately.

  • Estimating first and calculating second is the habit worth building.
  • Most useful sums in daily life are approximations anyway.

How to practise

Do the sum in your head first and check with a calculator, rather than the other way around. Being wrong and seeing why is what builds the instinct.