MEPX
Chapter 8 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 8 of 11

Squares and roots

A short list that pays for itself.

Worth memorising

The squares from 11 to 20: 121, 144, 169, 196, 225, 256, 289, 324, 361, 400. Recognising 169 as 13 squared saves the whole calculation.

  • Square roots of non squares sit between two you know: the root of 150 is between 12 and 13.
  • Squares end in predictable digits, so a number ending in 2, 3, 7 or 8 is never a perfect square.

Powers of two

1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024. Two to the tenth is 1024, the number behind kilobytes, and every doubling after that is worth knowing for sizes and capacities.