MEPX
Chapter 8 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 8 of 11

Elimination grids

The classic five houses puzzle.

Set up a table

Draw a grid with each category on an axis and mark cells as impossible when a clue rules them out. Certainty usually arrives from what has been eliminated rather than what was stated.

  • Mark both consequences of every clue: a yes in one cell means no across its row and column.
  • Reread the clue list after each deduction. Earlier clues say more once you know more.

Ordering clues

Clues like "A is somewhere left of B" constrain positions without fixing them. Work out the possible arrangements first, then apply the exact clues to cut them down.