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By elliekrezz
Question: You are trapped in a room with only one option of exiting: choosing between two doors. One door is blue and the other is red. One door will lead you to your freedom, the other to your death. You have a 50% chance of choosing the one that will lead to your freedom. You don't know which one is which. The doors are guarded by two guards. You can ask these two guards one question, and it must be the same question, so whatever you ask to one guard, you must ask the other the same one. One guard will always lie, and the other guard will always tell the truth. You don't know, again, which one lies and which one tells the truth. To choose the door that leads to freedom, what single question would you ask?
Answer: You would ask, "If I want freedom, what door will he say I should go through?" You will ask this to both guards. For eg, let's say the door to freedom is the blue door (pretend you don't know this). If you ask the lying guard, he will tell you the truthful one wants you to go through the red door, which is a lie, since the truthful guard would tell the truth saying you should go through the blue. When you turn to the truthful guard, he will truthfully say that the lying guard wants you to go red door, the one that is not freedom and a lie since that is not the door you asked for. Therefore, you can conclude that the door is the blue door. You won't be able to tell which one's the truthful one or the lying one, all that matters is that the blue one is out of option. (Vice versa if the door is actually red, both guards would then say blue.)
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