How to Find Direction?

Two men stand at a fork in the road. One fork leads to Town A; the other fork leads to Town B. One of these people always answers the truth to any yes/no question which is asked of him. The other always lies when asked any yes/no question. Both of them knew which road leads to which? By asking one yes/no question, can you determine the road to Town A?


Answer:

The fact that there are two men is a red herring - you only need one of them. Ask either of them the question:
"If I ask you if the left fork leads to Town A, will you answer 'yes'?"
If the person asked is a truthteller, he will answer "yes" if the left fork leads to Town A, and "no" otherwise. In the event of the person asked is a liar and if the left road does not lead to Town A, still the liar will tell "yes". So irrespective of whether the person is a truthteller or a liar, if he says "yes", we can safely take the left road to Town A. If the answer to the question is a "no", take the other one, the right road.

Note:

In is interesting to note that the above problem can be formulated into a different shape by telling that only one person standing at the fork, whose nature (i.e. truthteller or a liar) we don't know and still can determine which road leads to Town A, by just asking one question.






So, either way, go left if the answer is "yes", and right otherwise.