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Finding sets, listing sets (discrete math)

  1. Jan 31, 2007 #1
    1. The problem statement, all variables and given/known data
    2. Let A, B and C be the following sets:

    A = (x є N | x< 25) B=(x e N | x = 2m for some positive integer m)
    C = (x є N | x = 3m for some positive integer m)

    Find each of the following sets. In each case, list all of the elements of the set.

    i) A – (B u C) ii)A n C

    2. Relevant equations

    3. The attempt at a solution

    in my last post i have noticed i can't get the answers all done for me (which i understand) so i am pulling an all nighter.. and doind eatch question step by step.. seeing if maybe you all could help me out on this night

    A = 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25...
    B = 2,4,6,8,10,12,14,16,18,20,22,24
    C= 3,6,9,12,15,18,21,24

    there for
    A= {1,5,7,11,13,17,19,23}

    i donm't know how i would write that out clearly.. or even if that is right.. heh
  2. jcsd
  3. Jan 31, 2007 #2


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    Homework Helper

    First of all, what is the difference between the relations '<' and '[itex]\leq[/itex]'?
  4. Jan 31, 2007 #3


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    Staff Emeritus
    Science Advisor

    ??? You meant "N" didn't you?

    Why are you stopping at 24? The problem tells you that the points in A are less than 25, but not for B and C. (Since the sets you want are subsets of A, this doesn't really change your answer.)

    Why "therefore"? Yes, this is correct- it follows directly from the definition f A, not what you just wrote.

    Assuming that you really meant N for the first, your set A is correct. For B and C, you are missing the "{ }" symbols and need to continue them:
    B= {2, 4, 6, 8, 10, 12, 14, 16, 18, ...}
    C= {3, 6, 9, 12, 15, ...}

    Now, what is "BnC"? What is BuC?
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