You are trapped in a room with two doors one leading to freedom and the other to death There are two computers one always lies and one tells the truth What one question could you ask them to escape?

Answer 1

The puzzle is based on only being able to ask one question of either computer

and receive one answer. The question, asked to either computer, is "What

would the other computer say is the way to freedom?"

The one that lies would try to send you the wrong way, knowing that the

other computer can only tell the truth, and would tell you the right door.

The one that tells the truth would also tell you the wrong door, because it is

telling you what the lying computer would say.

Whichever computer answers, choose the OTHER door and you will gain freedom.

This is based on the Liar's Paradox, where someone who *always* lies cannot

say "I am lying." Here, knowing the computers' programming, you know that

neither of them can provide the correct (truthful) answer.

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Alternative #2:

Walk up to either computer, point to either door, and say:

If I were to ask you "Does that door lead to freedom?",

would you say "yes" ?

You don't have to know which computer you're talking to, and even after you

escape, you won't know which it was. But regardless of whether you're talking

to the lying computer or the truthful one, the anwer you get will tell you the

truth about the door to which you decided to point.

This is because the lying computer would lie about the lie he would tell you (a lie about a lie is the truth) and the truthful computer would of course tell you correctly.

(This is also the answer to a variation on the riddle, where there is only one answerer who either always tells the truth or always lies, and you do not know which it is.)