Puzzles
Three doors, one car
A car is behind one of three doors; goats behind the other two. You pick door 1. The host — who knows where the car is — opens door 3, revealing a goat, and offers you the chance to switch to door 2. Should you?
Reveal the answer
Switch — it doubles your odds, from 1/3 to 2/3. Your first pick was right 1/3 of the time, and the host's reveal concentrates the remaining 2/3 onto the other closed door. When Marilyn vos Savant published this, thousands of readers — including maths PhDs — wrote in to insist she was wrong. She wasn't.