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Homework Help: Probability question I can't work out

  1. Feb 25, 2010 #1

    I've just joined here and I'm doing some revision on conditional probability. This one question, which I know should be simple, has me stumped. I've tried what I can think of but I can't seem to get it right. Any help anyone may have would be very much appreciated.

    Suppose A and B are events and de ne the new event C to occur if and only if
    exactly one of A or B occur. Show algebraically, using only the probability axioms and
    properties, and basic set-theoretic results given in the lectures, that
    Pr(C) = Pr(A) + Pr(B) - 2Pr(A n B)

    Thank you
  2. jcsd
  3. Feb 25, 2010 #2


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    Science Advisor

    C=(A-B) or (B-A), which are mutually exclusive events.. Evaluate probabilities to get result.
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