You’re a logician who wants to know which of two roads leads to a village. Standing nearby, inevitably, are three natives: one always lies, one always tells the truth, and one answers randomly. You don’t know which is which, and you can ask only two yes-or-no questions, each directed to a single native. How can you get the information you need?
Ask native A, “Is B more likely than C to tell the truth?” Then go to the native he indicates is less trustworthy and ask, “If I were to ask you whether this road goes to the village, would you say yes?”
This procedure ensures that you won’t put the second question to the random answerer. Once that’s sure, then you’re just facing the classic version of the puzzle, with one liar, one truth-teller, and one yes-no question.
