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Where can i find forum that solve these kind of questions

  1. Aug 11, 2008 #1
    its more of a logic question
    its used in my country in the "asat" exam
    i need to solve this kind of in a minute an a half
    the question is :
    mary bought ten books

    5 pairs of books
    each pair of books has its own colors
    a yellow pair ,a purple pair ,a black pair ,a blue pair, a red pair (10 books )
    she decided to arrange them on 4 shelves ,but there are rules for arranging them

    two books of the same color will not be on the same shelf
    a yellow book cannot be on the same shelf with a purple shelf
    a blue book will always be with a red book
    in each shelf the amount of books will not exceed 3 books

    what arrangement cannot happen if we know that on one self we have a purple and a blue books?
    A.there is another shelf which has a purple and a blue book on it
    B.there is a black book next to a red book
    C.there is a yellow book next to a black book
    D.there is a purple book next to a black book

    i need to choose one of the answers
    i am looking for a forum on this kind of questions
    where should i look for?
  2. jcsd
  3. Aug 11, 2008 #2


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    Note that given your instuctions, blue and red books must appear on the same shelves, and you therefore have that if you know there is a purple book with a blue book, then the last book on that shelf must be red.

    On another shelf, where the last blue book is, it is also a red book.

    Thus, you have two remaining "empty shelves" and one shelf with only one place left.

    How can you arrange the yellow books so that none of those two will appear together with the last purple one?
    In particular, what arrangements would have to be forbidden (remember that the two yellow books can't be placed on one shelf!)?
  4. Aug 11, 2008 #3
    ye the second answer is the correct one
    because the yellow will be with the purple
    where can i ask this sort of question?
  5. Aug 11, 2008 #4


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    Well, you will not be chastised, castrated or executed if you keep on posting in the General Maths forum. We are not evil people here at PF (not very, anyways..).

    But if you want the sub-forum which is most appropriate for puzzles of logic, you might either post in the set theory&logic subforum, or you could go into the Lounge sections and post under "Brain Teasers" (in General Discussion). That sub-forum is usually reserved as posting challenges to which you know the answer, but I'm sure some there can help you out if you don't know the answer beforehand.

    And, you picked the correct answer. :smile:

    Beware of fish if you venture into GD, though..
  6. Aug 11, 2008 #5
    where can i find theory&logic subforum

    i cant find it
  7. Aug 11, 2008 #6


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    Staff: Mentor

    Moved to Brain Teasers.
  8. Aug 11, 2008 #7


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    Directions to set theory & logic subforum:

    Starting at https://www.physicsforums.com ,
    click on "Mathematics"
    then click on "Set Theory, Logic, Probability, Statistics"
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