Home > Riddles > The guardianes of the two doors
One of the best-known versions of the truth-tellers and liars riddles. The beauty of it is that you don't need to find out who is telling the truth: just ask a question that turns both answers into the same red herring.
You are faced with two doors: one leads to the exit and the other to perdition. Next to them are two guardians.
One always tells the truth and the other always lies, but you don't know which is which. You can ask one of the guardians a single question.
What questions to safely choose the right door?
Answer: ask either of them: > “If I asked the other guardian which door was correct, which door would he point to?” Then choose the opposite door. If you ask the truthful guardian, he will honestly tell you what the liar would answer. The liar would point to the wrong door, so the truthful will also point you to the wrong door. If you ask the lying guardian, he will lie about what the truthful one would answer. The truthful person would point to the correct door, but the liar will point out the opposite: the wrong door. In both cases, the answer points to the wrong door. Therefore, you must choose the other.
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