You face two doors: one leads to freedom, the other to danger. Guarding them are twin brothers: one ALWAYS tells the truth, and the other ALWAYS lies. You may ask EXACTLY ONE question to ONE guard. What question guarantees you find the door to freedom?
Ask either guard: 'Which door would your brother say leads to freedom?' and then enter the opposite door.
The truthful brother will report the liar's false choice (danger). The liar will lie about the truthful brother's true choice (also pointing to danger). Since both guards will point to the danger door, choosing the opposite door guarantees freedom.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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