The Liar and the Truthteller brain teasers
Brain Teaser: 1/1
There are two doors in front of you. One is door A, the other door B. When you go through one door (if it is the bad one), you will be in debt for a million dollars. When you go through the other door (if it is the good one), you will gain a million dollars a day. You obviosly want to go through the good door, but you do not know if door A or door B is the good door. There are also two people. One of them is person 1, the other person 2. One of them always lies, the other always tells the truth. You do not know which is the liar or the truthteller. They only answer questions pertaining to the doors, and you may ask them only one question. Remember that you want the good door. So, what question would you ask, and who would you ask it to?
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You ask either one which door the other guy would say is the good door, and go through the opposite door. You can ask either one of them because either way, you would get the oposite door. So, let's say person 1 is the truthteller and person 2 is the liar. The good door is door A, and the bad one door B. If you asked person 1 (the truthteller) what person 2 would say is the good door, he always tells the truth so he says door B because that is what the liar would say. With this knoledge, you go through door A. The same goes with person 2 (the liar). If you asked him what person 1 would say is the good door, person 2 would know person 1 tells the truth and would say the good door is door A (which it is), therefore person 2 would say door B is the good door. You should, with this knoledge, go through door A.
You may want to draw this out, it is easier to understand that way.
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