MEPX
Chapter 5 of 11All chapters
  1. 1How puzzles trick you
  2. 2All, some and none
  3. 3If, then
  4. 4Common fallacies
  5. 5Number sequences
  6. 6Words into equations
  7. 7Rate and work problems
  8. 8Elimination grids
  9. 9Knights, knaves and self reference
  10. 10Reading exactly
  11. 11Building the habit

Chapter 5 of 11

Number sequences

A checklist for finding the rule.

Work through the list

Look at the gaps first. If the gaps are not constant, look at the gaps between the gaps. Then check whether each term is built from the two before it, or from its position.

  • 2, 6, 12, 20, 30 has gaps of 4, 6, 8, 10, so the next is 42.
  • 1, 1, 2, 3, 5, 8 adds the previous two, giving 13.

Other shapes

Try ratios for growth, alternating rules for zigzags, and the position number itself: 1, 4, 9, 16 is n squared and 2, 6, 12, 20 is n squared plus n.