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Twenty Questions
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Twenty Questions

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

Rules

One player is chosen to be the answerer. That person chooses an object in mind, but does not tell the other players what the object is. All other players are questioners. They each take turns asking a question which can be answered with a simple Yes or No. The answerer answers each question in turn. Sample questions coulds be "Is it in this room?" or "Is it bigger than a breadbox?"

If a questioner guesses the object, that questioner wins and becomes the answerer for the next round. If twenty questions are asked without a correct guess, then the answerer has stumped the questioners and gets to be the answerer for another round.

Popular Variants

The most popular variant is called "Animal, Mineral, Vegetable". In this version, the answerer tells the questioners at the start of the game whether the object is an animal, mineral, or vegetable.

Other versions specify than the thing to be guessed should in a given category, such as actions, occupations, famous people, etc.

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".

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.

The most effective way to play 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.

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