Here is a classic logic riddle with a small but important clue. Five men are in a room. Barack is reading, Joe is playing chess, George is painting, and Bill is at his desk. The question asks: What is the fifth man doing?
The intended answer
The fifth man is playing chess with Joe.
The key is the detail about Joe. Chess is typically a game between two opponents. If Joe is playing a game of chess with another person in the room, the unnamed fifth man is the natural candidate to sit across from him.
Why the clue works
Four activities are listed, but only one naturally involves a partner. Reading can be done alone. Painting can be done alone. Sitting at a desk does not tell us what another person is doing. Playing a face-to-face game of chess, however, normally involves two players.
That makes the fifth man’s activity a good inference rather than a new detail that must be added.
Is the answer guaranteed?
The riddle relies on a conventional assumption: Joe is playing chess against someone physically present. In real life, a person could play chess online, against a computer, or even study a position alone. So the question does not logically prove what the fifth man is doing.
Still, playing chess with Joe is the familiar intended answer because it makes use of the one activity that usually requires a second participant.
Share this riddle and ask someone which clue helped them solve it. Did they catch the chess detail first?
