You are to meet with two brothers. You know that one of them, named Bob, has a very important package for you. Unfortunately, you never saw Bob or his brother, and don't know who is who.

To make the matter worse, one of the brothers is a pathological liar who never tells the truth, while the other never lies. Not only do you not know which is the liar and which tells the truth, but also, you do not know wether Bob is the liar or not.

Upon meeting the brothers, you can ask one short question of either of the brothers (but not both) to establish with certainty which of the two is Bob. (It is possible to do this with a question of four to five words.)

What question would you ask?

(The solution is up but I'm going to restrain myself...)

I have no solution. I'm just here to confirm a few things:

1 - Bob has the package
2 - You have never seen Bob or his brother
3 - One of the brothers lies
4 - The other doesn't

Asking "Are you Bob?" would return you with "Yes" from both brothers if Bob's brother is the liar, and "No" if Bob's the liar.

Ahhh! My head's spinning! I'm no good at these! *bangs her head on the wall and prepares to read the solution*

Posted by Hazirah on 2002-08-03 23:19:39