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Math Help - Unions and Intersections

  1. #1
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    Unions and Intersections

    Union and Intersections
    Let A= {x|x is a prime factor of 720}
    Let B= {x|x is a prime factor of 330}

    Find
    a) A intersect B
    b) A union B
    c) A - B

    i don't know how to get the answers, is there an easy way to do this kind of problem?
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  2. #2
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    Re: Unions and Intersections

    List prime factors of 720 and 330 (without repetition). For a), write factors appearing in both groups. For b), join the two groups (again, write each number only once). For c), write factors of 720 that are not factors of 330.
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  3. #3
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    Re: Unions and Intersections

    so
    A intersect B = 2,3,5
    A union B = 2,3,5,11
    A - B = 11

    is that correct?
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  4. #4
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    Re: Unions and Intersections

    Intersection and union are correct. A - B is empty, but B - A = {11} (set elements are written between curly braces; 11 itself is not a set).
    Thanks from zhengcl86
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  5. #5
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    Re: Unions and Intersections

    hmm somewhat understandable thank you for the reply
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