Three Keys

Three Keys is a contestant or a married couple was presented with a choice of three keys, one of which unlocked anything from boxes (containing money, trip tickets, etc.) to cars. The host usually offers a sure-thing buyout consisting of a smaller prize package, which was offered once one of the "dud" keys was demonstrated. A variation of this game involved more than one contestant selecting a key (sometimes from four instead of three). In this case, more than one key could (and often did) open the item, and contestants could trade in their key for an unknown behind a curtain/box or a cash amount. This probability game gave rise to the Monty Hall problem.

Deciding whether an announced prize was real or imitation, and choosing a cash amount or a box/curtain as a substitute.