A logician vacationing in the Bahamas finds himself on an island inhabited by two proverbial tribes of liars and truth-tellers. Members of one tribe always speak the truth, while other always lie. He stands at the fork of a road (a Tee-junction) and has to ask a bystander which leg he needs to follow to reach the village. He knows not whether the native is a truth-teller or a liar. The logician thinks for a moment and then asks only one question. What does he ask?
Another solution- Pick a road and ask, “Will the other guy tell me that this is the right road to take to get to town?” If it’s the right road and you ask the truth teller, he’ll know that the liar will say no, and thus say no. If you ask the liar, he’ll know that the truth teller would says yes, so he’ll lie and say no. If the road was the wrong road to take, the truth teller will know that the liar would says yes, and thus say yes. If you ask the liar, he’ll know that the truth teller would say no, so he’ll lie and say yes.
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