The Consecutive Integer Game
David M. Clark · Mathematics Magazine · 2002
Two previously unacquainted contestants, Xeno (X) and Yvonne (Y), sit at a table facing each other and play a game. You are the referee. Once the spectators are all seated, you randomly choose two positive, consecutive integers and, with a black marker, write one of the numbers on Xeno's forehead and the other number on Yvonne's forehead. Each player can read the other's number but not his or her own. [For example, you give Xeno 2475 and Yvonne 2476. Xeno sees 2476 and knows that his number is either 2475 or 2477, but he doesn't know which.] The first player to figure out his or her own number wins. The game proceeds in rounds.