Don, Ron and John
Three men are standing in a horizontal line, one next to the other. You come up to them and your job is to found out the names of each of these men. The men's names are Don, Ron and John in no specific order. For the sake of the puzzle the men will be labeled as[left, middle, right]. You are to ask them a certain number of question which can ask them about their names and in the following format, such as you can ask left: Is Middle John? or Are you Don?. Also, You know that one of the men will always lie and other two will always tell the truth. What is the Minimum number of questions that you need to ask them in order to guarantee that you know each man's name?
Ask the man on the left "Are you Don?" then "Are you Ron?"
If he answers "yes" to both questions, he's John and the liar.
If he answers "no" to both question, he's John and tells the truth.
If he answers "yes" to one and "no" to the other, ask him "Are you John?".
If he says "yes," he's the liar and his name is whichever one he said "no" to.
If he says "no," he tells the truth and he is who he says he is.
So at this point, you've used either two or three questions to find out the name of the man on the left and whether or not he tells the truth. If he tells the truth, ask him about the man in the middle; if he's the liar, ask the man in the middle yourself. Either way, pick one of the two names that doesn't belong to the man on the left and ask if it belongs to the man in the middle. Since you can trust the answer, that'll tell you the names of both remaining men. So, a max of four questions.
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