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Math Help - puzzle, set theory or statistics or probability

  1. #1
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    Talking puzzle, set theory or statistics or probability

    Of hundred people who read at least one of the three movie magazines are surveyed to study the readership pattern. It is found that 80 read Filmfare, 50 read Stardust and 30 read Cineblitz. Five read all three. How many read exactly two magazines?
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  2. #2
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    First thing to do is to get rid of the 5 that read all three so your left with

    95 people. 75 read mag A. 45 read mag B. 25 read mag C.

    Total of 145 mag read by 95 people

    145 - 95 = 50

    therfore 50 people read exactly 2

    the other 45 read one
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  3. #3
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    This is classical inclusion - exclusion principle.
    http://en.wikipedia.org/wiki/Inclusi...sion_principle

    100 = 80 +50 + 30 - (people who read two magazines) + (people who read three magazines)

    100 = 165 - (the number you are looking for)
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