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I came across this question, which I believe cannot be satisfactorily answered, but I'm not completely sure. Can you tell me if it has a answer?

If you choose the answer to this question at random,
what is the chance that you will be correct?
a) 25%
b) 50%
c) 60%
d) 25%
Bernard
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    Possible duplicate of [Multiple-choice question about the probability of a random answer to itself being correct](https://math.stackexchange.com/questions/76491/multiple-choice-question-about-the-probability-of-a-random-answer-to-itself-bein) (for reviewers: only option (c) is different from the duplicating target, but 60% clearly doesn't make more sense than 0%) – YuiTo Cheng Apr 07 '19 at 09:35

1 Answers1

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Correct (on the typical assumptions we can only pick one answer, that the selection is uniformly random, etc.). The question is actually a fairly common paradox. The cause is the sort of self-referential nature of the question.

  • Typically for multiple-choice questions with four answers, at random there is a $25\%$ chance to get it right. But two answers have that choice.

  • So logically it would be $50\%$, but only one choice corresponds to that. So you're damned if you pick either one: if $50\%$ is correct, the odds are $25\%$ and if $25\%$ is correct the odds are $50\%$.

  • $60\%$ simply makes no sense, being not a multiple of $25\%$, and can be ruled out outright.

So as it is posed, there is no correct answer.

Eevee Trainer
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