The Honest and Dishonest Guards

[Jazzy]

You’re in a room with two doors. There’s a guard at each door. One door is the exit, but behind the other door is something that will kill you. You’re told that one guard always tells the truth and the other guard always lies. You don’t know which guard is which. You are allowed to ask one question to either of the guards to determine which door is the exit.

What question should you ask?

 

[Nebulous]

These rules create a situation where there is no method for discerning one guards' honesty from the other, and thus which door leads to freedom. :s

I'd just pick a door without bothering to talk to the guards. As with any decision in life, there's always a risk things won't turn out the way you want.

 

[death180]

Yea screw it, just pick a door and go for it, trust your instincts. Don't rely on other people to help, because 50% of the time they're wrong.

 

[Sinon]

"Which door would the other guard tell me is the exit?"

The guard who always lies will point to the bad door (because he'll lie about the other guard's intentions), and the guard who tells the truth will point at the bad door too, because the liar wants you to die. So then you just take the other door.

It's similar to another riddle I've heard.

 

[Elvira]

I wanna watch Labyrinth now!

 

[Nebulous]

I wanna watch Labyrinth now!

Heh, yeah there's a scene similar to this in the movie.

 

[Elvira]

"One of these doors leads to the center of the labyrinth, the other to certain death. " Like that lol. Or close.

 

[Jazzy]

"If I had asked the other guard which door was the correct door, which door would he have pointed to?"

They will both give the same answer (indicating the wrong door). If you're talking to the guard that tells the truth, he will (truthfully) indicate the door that the other guard would have steered you towards which would be the wrong door, as the other guard always lies. But if you're talking to the guard that always lies, then he would still point to the wrong door, as while the other guard (the truth-teller) would have indicated the correct door, the guard you're speaking to is lying to you about what he would have said! So either way, the answer to your question will be the wrong door and so, either way, you simply use the other door.

 

[Elvira]

If Sarah had only known that!