There’s a growing class of puzzles I call Mensa Correctional Facility puzzles. In these puzzles there is always a warden who challenges prisoners with math/logic puzzles and grants them freedom when they succeed in solving them. Does anyone know the origins of the following one: In this puzzle the warden challenges a pair of Mensa inmates. The first inmate is shown to the warden’s room and the warden proceeds to place identical coins, each one either heads up or tails up, onto the 64 squares of a checkerboard. He then points to one of the coins and declares it to be the “freedom coin”. The inmate watching this is then invited to flip one of the coins to help his partner identify the freedom coin. Then, without allowing the inmates to communicate with each other, the second inmate is lead into the room, shown the coins, and after a little head scratching points to the freedom coin — he is, after all, a Mensa inmate — and the prisoners are set free. How did they do it? -Veit