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I stumbled over a probability paradox on the internet:

If you choose an answer to this question at random, what is the chance that you will be correct?

A) 25%

B) 50%

C) 60%

D) 25%

Given that "at random" means choosing each option with equal probability, each option had a chance of 25% to be correct. But since there are 2 options with 25% as the solution, we get 50% of being correct. In this case, B) would be correct. But then again, the probability of choosing B) at random would be 25%. And so on.

Does this paradox have a name? Is there something I can read on it?

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Terry
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    It's a self-referential paradox, much like "This sentence is a lie". It's popular enough, but I don't know whether it has its own name. – Arthur Jun 08 '17 at 07:35
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    How is this a paradox? Would it be a paradox if the choices were A)90% B)92% C) 95% D)98%? Do you consider a multiple choice question to be a "paradox" if none of the listed answers is correct? – bof Jun 08 '17 at 08:28
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    @bof the case you've presented wold be 'a question with set of answers not containing the right answer'. The answers in question are also without the right answer (0%), but if we change an answer C)60% to C)0%, then:

    if the right answer is $k%\not\in {0%,25%,50%}$, then the right answer is 0%, then the right answer is 25%, then the right answer is 50%, then the right answer is 25%...

    And we obtain a never ending chain

     – Jaroslaw Matlak Jun 08 '17 at 08:58
  • The given question has 0% in the body but the one with 60% is also answered there. – kingW3 Jun 08 '17 at 10:34
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    I would say this is not a duplicate, at least not of the linked question, since this question is not about explaining the paradox, but rather a reference request to whether this specific paradox has a name. – Arthur Jun 09 '17 at 20:45

1 Answers1

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Actually the answer to your question is not contained in possible answers -$0\%$

If we change an answer C)60% to C)0%, then:

If the right answer is $k\%\not\in \{0\%,25\%,50\%\}$, then the right answer is 0%, then the right answer is 25%, then the right answer is 50%, then the right answer is 25%...

The phrase you are looking for is Antinomy.

Jaroslaw Matlak
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