Riddle 1

I found this Riddle Archive via a link on Slashdot. I will be posting a few of them here.

Of three men, one man always tells the truth, one always tells lies, and one answers yes or no randomly. Each man knows which man is who. You may ask three yes/no question to determine who is who. If you ask the same question to more than one person you must count it as question used for each person whom you ask. What three questions should you ask?

Update: I was very embarrassed last night when I realized that my answer was incorrect. I’ll be sure to post an answer when I figure it out.

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17 Responses to Riddle 1

  1. amy says:

    did you get the answer?? i can’t figure it out. it seems kind of impossible if one of the three is _randomly_ answering..

  2. amy says:

    muahahahah! i think i figured it out. but it’s still kind of a badly worded riddle… also, kind of sneaky…

  3. Robert says:

    I have no idea what the answer is! The random guy really throws me – he could consistently answer like the truth teller or the liar and would be indistinguishable.

  4. amy says:

    heh.. you want the answer? or a hint?

  5. Robert says:

    Are you going to make me beg for an answer? :-)

  6. amy says:

    heh.. no, i just didn’t want to post the answer unless you wanted to read it. some people hate to have answers given to them.. (i’m generally not one of them, LoL!)

    answer: first of all, the three men will be known as A, B and C. we don’t know which is which. The truth teller will be referred to as T, the liar as L, and the random answerer as R.

    the basic principle i used: one must actually know the truth in order to tell it or to lie about it.

    so, we need to pose a question to A that he cannot possible know the answer to, ie: “will B and C both answer my question truthfully?” the only person who can give an answer is R. Neither T nor L know the truth, thus they cannot answer the question, either yes or know.

    So, if A is R, then you will get a yes or no. Now you just need to determine if B is T or L. This can be done with a simple question such as “Are you a male?”.

    If A is T or L, they will be unable to answer, now you need to determine if A is T or L. Do this the same way as above. If A is T, simply ask them is B is the one who always lies. If A is L, ask them if B always tells the truth, if they answer yes, then B is R, if they answer no, then B is T.

    :)

    there are probably a few other ways to do this.

  7. Robert says:

    That way would certainly work. I’ve since figured out another way (with a little help from someone else).

    You can ask compound questions. If you ask the right question, the single “Yes” or “No” will give you enough information to determine who is not random.

    If you ask A “Is either B the truth teller or C the liar?”, an answer of “No” will establish one of the following permutations: RTL, RLT, LTR, TLR. “B” is not random. An answer of “Yes” would establish RTL, RLT, LRT, TRL; C would not be random.

    You can then ask the non-random person a trivial question (“Do you answer randomly?”) to determine if he always lies or always tells the truth, and then ask him about the identity of one of the other two guys.

  8. amy says:

    i think your answer is probably more correct then mine.. mine seems to kinda bend the rules.. hehe…

  9. sssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuppppppppppppppppppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiidddddddddddddddddddddddddddddd

  10. sssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuppppppppppppppppppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiidddddddddddddddddddddddddddddd

  11. sssssssssssssttttttttttttttttttttuuuuuuuuuuuuuuppppppppppppppppppppppppppppppppppppiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiidddddddddddddddddddddddddddddd

  12. John says:

    I had the hardest time trying to find the simpliest answer for this riddle:

    There were two roads one leads to death the other leads to riches.( suffering or happiness) Ahead you see a cabin and in there lives twin brothers. One is Good and One is evil. You are allowed to ask 1 question what would it be?

    Since they look identical, you can’t figure out which ones lying or not.

  13. Mohsin Khan says:

    “If A is T, simply ask them is B is the one who always lies. If A is L, ask them if B always tells the truth, if they answer yes, then B is R, if they answer no, then B is T. ”

    but you don’t know which is which. how will you decide if A is T or L.

  14. Joe Wilger says:

    Ask any brother – “If I ask the other brother which way leads to happiness, which would he say?

    If you are talking to the truth teller, the other is a liar. That liar would point to death, saying it is safe. So the truth teller points to death, as well.

    If you are talking to the liar, the other is the truth teller. That truth teller would point to Life, saying it is safe. However, this brother lies, and points to death.

    Either way, they both point to death, and you take the path that they DON’T point to.

    Joe, Whittier CA
    PS. Got this from an old Dr. Who (starring Tom Baker). Pyramids of Mars, circa 1975.

  15. bright says:

    i am an object with a long tail.the longer the distance i go,the shorter my tail becomes

  16. Anonymous says:

    i am an object with a long tail.the longer the distance i go,the shorter my tail becomes

  17. psu lions says:

    a comet.

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