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Math Help - logicsets 3

  1. #1
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    logicsets 3

    can anyone do this question, im really stuck:

    Alan, Barbara, Charles ara chooses Colin Dexter
    and Jane Austen, Charles chooses dicck Francis, Colin Dexter and Terry Pratchett, and Deborah chooses Jane Austen and Terry Pratchett.

    (a) Denoting the shere l, d, a, f and p stand for Robert Ludlum, Colin
    Dexter, Jan
    above.

    (b) Explain w between people and authors.

    (c) Use projection and inverse projectiochosen by Barbara.


    (d) Use projectssion for all the readers choosing both dicck
    Francis and Robert Ludlum.

    thank you
    Last edited by srk619; November 19th 2008 at 11:32 AM.
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  2. #2
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    Quote Originally Posted by srk619 View Post
    can anyone do this question, im really stuck:

    Alan, Barbara, Charles and Deborah each have to pick two authors they read.
    Alan chooses Robert Ludlum and Colin Dexter, Barbara chooses Colin Dexter
    and Jane Austen, Charles chooses dicck Francis, Colin Dexter and Terry Pratchett, and Deborah chooses Jane Austen and Terry Pratchett.

    (a) Denoting the set of people by P = {A, B, C, D} where A, B, C and D stand
    for Alan, Barbara Charles and Deborah respectively and the set of authors
    by A = {L, d, a, f , p}, where l, d, a, f and p stand for Robert Ludlum, Colin
    Dexter, Jane Austen, dicck Francis, and Terry Pratchett respectively, give a
    relation (i.e. a subset of P x A) which encapsulates the information given
    above.

    (b) Explain why it is not possible to use a function from P → A or a function
    from A → P to give the relationship between people and authors.

    (c) Use projection and inverse projection mappings to give an expression for
    the names of all the authors chosen by Barbara.


    (d) Use projection and inverse projection mappings together with set algebraic
    operations to given an expression for all the readers choosing both dicck
    Francis and Robert Ludlum.

    thank you


    The relation is:

    R={ (A,l),(A,d),(B,d),(B,a),(C,f),(C,d),(C,p),(D,a),(D ,p)}.


    Now we cannot have a function from P to A, BECAUSE one of the conditions that must be satisfied by a function is that:


    No two ordered pairs have the same 1st member.

    And in our case we do have two ordered pairs with the 1st member,

    [ (A,l),(A,d) ]
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  3. #3
    Junior Member
    Joined
    Nov 2008
    Posts
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    help

    i can do the mapping but i dont know how to
    set algebraic
    operations to given an expression for all the readers choosing both dicck
    Francis and Robert Ludlum.
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