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Math Help - Reasoning word problem

  1. #1
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    Reasoning word problem

    Hey everyone could someone please tell me if im on the right path?

    knights always tell the truth
    Knaves always lie

    Two natives C and D approach you but only C speaks

    C says: Both of us are knaves
    What are C and D

    My work---------

    suppose C is a knave
    C always lies
    C and D are not knaves
    then C and D are knight


    Next q You encounter natives E and F
    E says: F is a knave
    F says: E is a knave

    My work ------
    suppose F is a knave
    F lies
    E is a knight
    E tells the truth
    therefore F is a knave

    suupose E is a knave
    E lies
    F is a knight
    F tells the truth
    therefor E is a knave??



    Thankl you
    Last edited by Thetheorycase; September 22nd 2010 at 06:43 PM.
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  2. #2
    MHF Contributor undefined's Avatar
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    Quote Originally Posted by Thetheorycase View Post
    Hey everyone could someone please tell me if im on the right path?

    knights always tell the truth
    Knaves always lie

    Two natives C and D approach you but only C speaks

    C says: Both of us are knaves
    What are C and D

    My work---------

    suppose B is a knave
    C always lies
    C and D are not knaves
    then C and D are knight


    Next q You encounter natives E and F
    E says: F is a knave
    F says: E is a knave

    My work ------
    suppose F is a knave
    F lies
    E is a knight
    E tells the truth
    therefore F is a knave

    suupose E is a knave
    E lies
    F is a knight
    F tells the truth
    therefor E is a knave??



    Thankl you
    After some time I can understand what you were thinking, there is a typo where you wrote B instead of C, also you incorrectly negated the statement "we are both knaves" obtaining "we are both knights" whereas the real negation is "at least one of us is a knight".

    I recommend making a table

    Code:
    C D Possible
    ============
    I I N
    I A N
    A I Y
    A A N
    I stands for knight, A stands for knave, and the third column is whether it's possible for C to say "we are both knaves". (C,D) = (A,I) is the only possibility.

    For the second one you get to the answer but don't seem to know it. Based on what E says, E being a knave implies F is a knight, which is consistent with what F says. And vice versa. But it's much clearer to write in table form.

    Code:
    E F Possible
    ============
    I I N
    I A Y
    A I Y
    A A N
    The two possible solutions are (E,F) = (I,A) and (E,F) = (A,I).
    Last edited by undefined; September 22nd 2010 at 06:50 PM.
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  3. #3
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    Thank you .. Alot clearer
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