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Two Guards and Two Doors

Easylogic

This Easy puzzle in the “logic” category rewards careful reading and step-by-step reasoning. Use the hint if you are stuck, then compare your approach with the explained answer.

You are trapped in a room with 2 doors.

One door leads to freedom, and the other leads to certain doom.

There are also 2 guards:

  • One guard always tells the truth
  • The other always lies

You may ask one yes-or-no or one normal question to one guard.

What should you ask to guarantee you choose the correct door?

Show Hint
Ask a question where both guards are forced to point to the wrong door.
Show Solution

Ask either guard: “Which door would the other guard say leads to freedom?”

Then choose the opposite door.

Why?

  • If you ask the truthful guard, they truthfully tell you the lie the other guard would say.
  • If you ask the lying guard, they lie about the truthful guard’s answer.

In both cases, the guard points you to the wrong door.

So the correct strategy is to ask what the other guard would say, then pick the opposite door.

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