The Fatal Labyrinth of Simple Questions
Logic
Level
1
The Labyrinth
- At the end of a labyrinth, there are three doors: Only one of them lead you to safety, the other two lead to pits of lava.
- And guarding them are three guards: one who always tells the truth, one of them always lies and the third guard kills you if you ask a trick question, but otherwise is truthful. You do not know which guard is which.
-
The following questions are considered trick questions:
- A self referential question. E.g, Is the answer to this question no?
- A question about any of the guards. E.g, Is the guard to your left a liar?
- A question involving a possible question. E.g, Would you say yes if I asked you whether this door is safe?
Can you ask exactly one question to exactly one of the guards to find out which guard is truthful?
Yes
No
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Ask all of the guards at the same time, "Do you kill people who ask trick questions?" The liar will say yes, as he has to lie. The guy who kills people will say yes, as he does kill people who ask trick questions. The truth-teller will say no, as he does not kill people who ask trick questions.
So whoever says no is the truthteller.