Twenty Questions

Twenty Questions is a popular spoken parlour game for two or more players. It encourages deductive reasoning and creativity.

Trivia

• The game was turned into a popular radio game show by the BBC in the 1950s. The object to be guessed was revealed to the audience by a "mystery voice". This format was briefly used again on Radio 4 in the 1990s but only lasted one series. A TV version was also made by Associated-Rediffusion in the early 1960s. The "mystery voice" used on the original radio series gave rise to a running joke on the radio series I'm Sorry I Haven't A Clue.
• A version of Twenty Questions is played as a parlor game by characters of Charles Dickens' A Christmas Carol.
• Game theory suggests that the information (as measured by Shannon's entropy statistic) required to identify an arbitrary object is about 20 bits. The game is often used as an example when teaching people about information theory. Mathematically, if each question is structured to eliminate half the objects, twenty questions will allow the questioner to distinguish between 2²⁰ or 1,048,576 objects. Accordingly, the most effective strategy for Twenty Questions is to ask questions that will split the field of remaining possibilities roughly in half each time. The process is analogous to a binary tree search algorithm in computer science.