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Math Help - Probability

  1. #1
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    Probability

    Our city has 2400 subscribers for HipHop magazines Of these, 1200 subscribe to Magazine A, 500 subscribe to Magazine B, and 100 subscribe to both. What is the probability that a subscriber selected at random subscribes to either Magazine A or B?


    If I add the subscribers of magazine A and B together (which is 1700), and divide it by the total amount of subscribers then I get a very small fraction, which isn't right. I think.
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  2. #2
    Senior Member tukeywilliams's Avatar
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    You are trying to find  P(A \cup B) = P(A) + P(B) - P(A \cap B) or  \frac{1200}{2400} + \frac{500}{2400} - \frac{100}{2400} = \frac{1600}{2400} = \frac{2}{3} .
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  3. #3
    Eater of Worlds
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    P(A)+P(B)-P(A \;\ and \;\ B)

    See how it's done?. You have to subtract the 100 they have in common. Otherwise, you'd over count.

    \frac{1200}{2400}+\frac{500}{2400}-\frac{100}{2400}
    Last edited by galactus; November 24th 2008 at 05:39 AM.
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