When you are trying to get to Truth Town, you get to No Knaves Town, a city comprised of only Liars and Knights. Each of the three forks leading away from the town (not including the one you came from) leads to a different city.

There are 6 people around. Wanting to know who is what so you can ask them which fork to take, you ask them who is a liar and who is a knight.

A: C would say that B is a liar
B: D would say that C is a knight
C: E would say that F is a liar
D: C would say that A is a knight

Tired of these responses, you ask what fork leads to Truth Town.

E: The left fork leads to Truth Town
F: The middle fork leads to Truth Town

Which fork should you take to get to Truth Town?

The problem can be easily solved by only considering what C, E, and F say, given the knowledge that the problem is solvable.

If C is telling the truth, then one of E or F is telling the truth and the other is lying. However we have no way of determining which of them is the truth teller and which one is the liar, so the problem would not be solvable if this is the case. (Note that A,B, and D never mention E or F, so we can disregard everything they say).

So we conclude that C must be lying. So either both E and F are telling the truth (which would be contradictory), or both are lying, which means the Right fork is the one to take, which is the answer.

Posted by Avin on 2004-11-01 16:53:32