You are at one end of a hall blindfolded. At the other end are Alex and Bert. You are allowed to ask any yes or no questions you want, but only one of them will respond. They are standing next to each other and their voices are identical, so you have no way of telling which one responded by sound alone.

Using as few questions as possible, find out the type of each Alex and Bert and who answered your last question.

(In reply to another try by rerun141)

rerun141: "penny's question doesn't establish who's the liar and who's the knight...."

Right. Let me try again....

Two questions:

If I were to ask you if you were Alex, would you say yes?
If I were to ask you if you were a liar, would you say yes?

If the answers are "yes, yes", liar Alex has answered.
If the answers are "yes, no", truthteller Alex has answered.
If the two answers are "no, yes", liar Bert has answered.
If the answers are "no, no", truthteller Bert has answered.

Posted by Penny on 2003-12-30 15:32:41