Puzzles
Four cards, one rule to test — which two do you actually need to flip?
Four cards lie on a table, each with a number on one side and a color on the other. You can see: 3, 8, blue, red. To test the rule 'if a card shows an even number, its other side is blue,' which card or cards must you turn over?
Reveal the answer
The 8 and the red card. Most people wrongly pick 8 and blue — but blue can't disprove the rule even if its other side is odd, while the red card could disprove it if its other side turns out even. Psychologist Peter Wason devised the test in 1966; only 10-20% of people solve it correctly, though success jumps sharply when the same logic is dressed up as a social rule, like checking IDs at a bar.