At the last phase of a treasure hunt, you finally reach up to a place where you see two closed doors. You know that one of the doors have the treasure behind, the other has painful death. Each door has a security guard in front of it. You also know that one of the guards always tell the truth, and the other always lies-- but they look identical and you don't know who is the truthful guy. then, how would you determine which door has the treasure ? At the last phase of a treasure hunt, you finally reach up to a place where you see two closed doors. You know that one of the doors have the treasure behind, the other has painful death. Each door has a security guard in front of it. You also know that one of the guards always tell the truth, and the other always lies-- but they look identical and you don't know who is the truthful guy. You are allowed to ask only one of them only one question. Then, how would you determine which door has the treasure ?
11-Ans- Just ask any one of them "If I ask the other guard which one is the treasure-door which door would he have shown ?".
If you ask this question to the truthful guy he would think "The other guy is a liar, thus he would have shown the wrong door", and that's why the truthful guy will show you the wrong door.
If you ask this question to the liar guy he would think "The other guy is truthful, thus he would have shown him the correct treasure-door, so I'm going to tell him the opposite one and I'll show him the wrong door", and that's why the liar guy will also show you the wrong door.
Thus, it does not matter who you ask the question, the answer will always point to the wrong door-- you know it, hence go to the other door and get the treasure !