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?
(In reply to solution
You ask "Who would your brother say is bob?". This would lead to a lie each time and so you would then know that the opposite is true.
Ahh, finally an original answer! Why do countless other people who know the answer never look to see if others have answered with the exact same solution?
Posted by Sam
on 2003-09-22 00:34:38