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Homework Help: Set theory: find the intersection

  1. Nov 23, 2013 #1
    1. The problem statement, all variables and given/known data

    In a group of 30 people each person twice read a book from books A, B, C. 23 people read book A, 12 read book B and 23 read book C.

    (a) How many people read books A and B?
    (b) How many people read books A and C?
    (c) How many people read books B and C?

    2. Relevant equations

    3. The attempt at a solution

    I'm not sure how to start. Any hints will be very much appreciated.
    Thank you
  2. jcsd
  3. Nov 23, 2013 #2


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    Homework Helper

    There seem to be errors with this problem. For example, the problem is symmetric in A and C, so parts (a) and (c) are really the same question. And usually people don't read the same book twice but that seems to happen here. I would ignore this problem for being unclear or having errors.

    Also, in the current form it looks prohibitively difficult to solve, suggesting that there is a mistake.
  4. Nov 23, 2013 #3


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    Staff: Mentor

    Welcome to the PF

    Please check your PMs -- you *must* show some effort toward solving the problem before we can offer tutorial help
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