Truthtellers and Liars

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  • Banfa
    Recognized Expert Expert
    • Feb 2006
    • 9067

    Truthtellers and Liars

    I'm sure you've all heard this one
    You come to a T junction, 1 road leads to certain doom in the pit of invalid memory accesses while the other leads to a chocolate mountain (or in mmccarthy's case a Whiskey Lake). There are no sign posts but there are 2 people at the cross roads, one is wearing a red T-shirt and the other is wearing a blue T-shirt.

    There is a wooden sign saying, "1 person always tells the truth and the other always lies. But we are not telling you who is who. Meuuuuuuuuu Ha Ha Haaa".

    You can not go back the way you came because you are being chased by a BOFH.

    You may ask 1 question that can be answered yes or no (you don't know how you know this, the knowledge just appeared in your mind as you took in the scene. Almost as if it was POKEd there).

    What question should you ask to find out which path to take?

    Like a said well known, in fact it has even appeared in the odd film (Labyrinth), so if that was too easy for you try this one
    You come to a another T junction, 1 road leads to even more certain doom in the dungeon of middle managers while the other leads to the oasis of coffee and forgetting about work. There are no sign posts but there are 3 people at the cross roads, one is wearing a red T-shirt, one is wearing a blue T-shirt, and the last one is wearing a Hawkwind T-shirt.

    There is a wooden sign saying, "1 person always tells the truth, 1 person always lies and 1 person randomly answers yes or no. But we are not telling you who is who. MEEEEUuuuuuuuu Ha Ha Haaaaaaaaaaaaaa ".

    You can not go back the way you came because a particularly vicious virus is in the process of erasing that road.

    You may ask 2 questions that can be answered yes or no (you know this because floating above the scene is a bright pink flashing neon sign saying so).

    What questions should you ask of who to find out which path to take?
    Last edited by Banfa; May 13 '07, 02:26 PM. Reason: Removal of information defeating logic of questions
  • subashini Thiyagarajan
    New Member
    • Dec 2006
    • 218

    #2
    HI banfa,

    I don't know whether my understanding is correct.

    it is very easy

    i ll ask truth teller


    Is this(left) road leads to cholcolate mountain?


    Truth teller answer me yes or no
    so i ll go ahead

    if two question allowed
    i 'll ask lier the same question .if i get different answer with full confirmation i'll go ahead!!

    any comments

    Comment

    • Banfa
      Recognized Expert Expert
      • Feb 2006
      • 9067

      #3
      Originally posted by subashini Thiyagarajan
      HI banfa,

      I don't know whether my understanding is correct.

      it is very easy

      i ll ask truth teller


      Is this(left) road leads to cholcolate mountain?


      Truth teller answer me yes or no
      so i ll go ahead

      if two question allowed
      i 'll ask lier the same question .if i get different answer with full confirmation i'll go ahead!!

      any comments
      Yes I have a comment, I have completely written the questions wrong. Your solution works the way I originally wrote the questions but I am about to re-write them to actually be what they should be, then please try again.

      Comment

      • AdrianH
        Recognized Expert Top Contributor
        • Feb 2007
        • 1251

        #4
        Originally posted by Banfa
        Yes I have a comment, I have completely written the questions wrong. Your solution works the way I originally wrote the questions but I am about to re-write them to actually be what they should be, then please try again.
        I know the answer to your first question.

        The answer to the second one is not as clear. If I were ask the one in the red "what would the one in the blue say if I asked the one in the Hawkwind, ``does the left path lead to certain doom?''" and that person is not the random one, how will that one react? Will it ask the one in blue to ask the one in Hawkwind? Or will it not answer because it cannot do so without violating it's yes/no ability?


        Adrian

        Comment

        • Banfa
          Recognized Expert Expert
          • Feb 2006
          • 9067

          #5
          Originally posted by AdrianH
          The answer to the second one is not as clear. If I were ask the one in the red "what would the one in the blue say if I asked the one in the Hawkwind, ``does the left path lead to certain doom?''" and that person is not the random one, how will that one react? Will it ask the one in blue to ask the one in Hawkwind? Or will it not answer because it cannot do so without violating it's yes/no ability?
          You will always get an answer, if any one of the people in the chain of people involved in your question is the random answerer than the answer you get will be random.

          Comment

          • subashini Thiyagarajan
            New Member
            • Dec 2006
            • 218

            #6
            please repeat the correct question again

            i feel this is not to think a lot to answer ........

            Comment

            • Banfa
              Recognized Expert Expert
              • Feb 2006
              • 9067

              #7
              Originally posted by subashini Thiyagarajan
              please repeat the correct question again

              i feel this is not to think a lot to answer ........
              I edited the original posts to contain the correct answers.

              As a clue I will say that in both questions the people you meet at the T junction already know who each other are and how they will respond.

              Comment

              • Ganon11
                Recognized Expert Specialist
                • Oct 2006
                • 3651

                #8
                I have a creative answer to the first question;

                First step: Randomly punch one of the people. If you have punched the Truthful one, he will inevitably start screaming in pain, saying, "Ow, it hurts!" etc. etc. If you have punched the liar, he will vehemently deny that you hurt him at all. Either way, you will know who the Truthful one is.

                Second step: Ask the truthteller which way leads to certain doom, and take the other path.

                I'm the winner!

                Comment

                • AdrianH
                  Recognized Expert Top Contributor
                  • Feb 2007
                  • 1251

                  #9
                  Originally posted by Ganon11
                  I have a creative answer to the first question;

                  First step: Randomly punch one of the people. If you have punched the Truthful one, he will inevitably start screaming in pain, saying, "Ow, it hurts!" etc. etc. If you have punched the liar, he will vehemently deny that you hurt him at all. Either way, you will know who the Truthful one is.

                  Second step: Ask the truthteller which way leads to certain doom, and take the other path.

                  I'm the winner!
                  ROFLMAO. :D


                  Adrian

                  Comment

                  • Banfa
                    Recognized Expert Expert
                    • Feb 2006
                    • 9067

                    #10
                    Originally posted by Ganon11
                    I have a creative answer to the first question;

                    First step: Randomly punch one of the people. If you have punched the Truthful one, he will inevitably start screaming in pain, saying, "Ow, it hurts!" etc. etc. If you have punched the liar, he will vehemently deny that you hurt him at all. Either way, you will know who the Truthful one is.

                    Second step: Ask the truthteller which way leads to certain doom, and take the other path.

                    I'm the winner!
                    It is typical of a C++ programmer to approach a (fairly) elegant logic problem with brute force :p

                    Comment

                    • AdrianH
                      Recognized Expert Top Contributor
                      • Feb 2007
                      • 1251

                      #11
                      Originally posted by Ganon11
                      I have a creative answer to the first question;

                      First step: Randomly punch one of the people. If you have punched the Truthful one, he will inevitably start screaming in pain, saying, "Ow, it hurts!" etc. etc. If you have punched the liar, he will vehemently deny that you hurt him at all. Either way, you will know who the Truthful one is.
                      Ahhh, but what happens if these are ninja-kung-fu people. Then they'd whip yer ass. :D


                      Adrian

                      Comment

                      • tolkienarda
                        Contributor
                        • Dec 2006
                        • 316

                        #12
                        Answer to question one
                        Ask: "If i were to ask for the road to wisky lake what direction would the other person point right",
                        the liar will lie about the way the truth teller will point and then point to the bad place, and the truth teller will also point to the bad place. so of course go the oposite way they both point

                        eric

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