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You are at a crossroad. One road goes to hell, the other to paradise. There is one guard. The guard only answer questions and only using Yes or No. The guard is one of two categories: one category always lies, the other always tells the truth (but you don't know to which category the guard belong). You are allowed to ask only one question to decide which road to take.

Can you ask a single question to the guard and be sure to go to heaven? Note that you cannot ask about what another hypothetical guard could answer because you do not know which kind she or he could be.

This question differs from the two guard question because there is only one guard. You cannot refer to another guard.

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  • $\begingroup$ This seems to be a duplicate. Could you make sure that this puzzle has not already been asked? $\endgroup$
    – user79541
    Jan 27 at 16:03
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    $\begingroup$ Does this answer your question? Two doors with two guards - one lies, one tells the truth $\endgroup$
    – Jaap Scherphuis
    Jan 27 at 16:10
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    $\begingroup$ Since you only ask one question, it doesn't matter that one of the guards is missing. $\endgroup$
    – Jaap Scherphuis
    Jan 27 at 16:12
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    $\begingroup$ It's effectively the same question since you could ask rot13(Vs lbh jrer sebz gur bgure pngrtbel, juvpu ebnq jbhyq lbh gryy zr yrnqf gb urnira?) $\endgroup$
    – Mohirl
    Mar 28 at 10:58
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    $\begingroup$ @AlainDamlamian It's true that the question itself is different, but if you look at the answers to the linked question, the second and third highest scoring are also valid answers to your question because they don't refer to the second guard. $\endgroup$
    – Especially Lime
    Mar 28 at 15:08

1 Answer 1

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"When someone asks you whether the road on the left goes to Heaven, do you answer 'yes'?"

is a possible question.

- If the road goes to Heaven and the guard tells the truth, he will say yes.

- If the road goes to Heaven and the guard lies, he will say yes.

- If the road goes to Hell and the guard tells the truth, he will say no.

- If the road goes to Hell and the guard lies, he will say no.

In each case you can determine which road leads where and pick your favorite destination.

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