Brain Food Solution

This was the question:

Travelling to a city, an old man lost his way. He came to a fork in the road and did not know which road to take. Standing at the fork were two men. Next to the men was a sign, which you may assume is correct, which stated that one of the two men always told the truth and one of the men always told lies (but it was not known which was which). The sign went on to say that travellers could only ask one of the men one question.

And this is the solution:

Ask one of the men what the other man would answer to the question, "Is the left road the correct road?" Then assume the answer you are given is false and act on that knowledge.

If the man you ask is the liar, he'll incorrectly give you the truthful man's answer. If the man you ask is the truthful man, he'll correctly give you the liar's wrong answer. 

back