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Abrain teaser is a form ofpuzzle that requires thought to solve. It often requires thinking in unconventional ways with given constraints in mind; sometimes it also involveslateral thinking.Logic puzzles andriddles are specific types of brain teasers.

One of the earliest known brain teaser enthusiasts was theGreekmathematicianArchimedes.^[1] He devisedmathematical problems for his contemporaries to solve.

Q:If three hens lay three eggs in three days, how many eggs does a (statistical) hen lay in one day?

A1:One third. (Note: 3 hens = 3 eggs / 3 days → 3 hens = (3 / 3) (eggs / days) → 1 hen = (1 / 3) (egg / days))

A2:Zero or one (it's hard to lay a third of an egg).

One can argue about the answers of many brain teasers; in the given example with hens, one might claim that all the eggs in the question were laid in the first day, so the answer would be three.

Q:Mary's father has five daughters: 1. Nana, 2. Nene, 3. Nini, 4. Nono. What is the name of the fifth daughter?

A:Mary. The first four daughters all have names with the first 4 vowels, so if someone does not think about the question, they may say the name with the fifth vowel, Nunu. The answer was given at the beginning of the question (i.e.,Mary's father has five...)

Q:What appears once in a minute, twice in a moment, but never in a thousand years?

A: The letter "M".

Q:I am the beginning of the end, the beginning of eternity, and the end of all time?

A: The letter "E".

The difficulty of many brain teasers relies on a certain degree of fallacy in humanintuitiveness. This is most common^[2] in brain teasers relating toconditional probability, because the causalhuman mind tends to consider absolute probability instead. As a result, controversial discussions emerge from suchproblems. One of the famous brain teasers is theMonty Hall problem.^[3] Another (simpler) example of such a brain teaser is theBoy or Girl paradox.

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