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Math Help - probability of events

  1. #1
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    probability of events

    An auditor is erroneous 5% of the time when preparing financial statements. Suppose that he randomly checks 3 entries, find the probability that he makes
    a) 0 mistakes
    b) 1 mistakes
    c) 2 mistakes
    d) 3 mistakes

    for a) I know it's (0.95)(0.95)(0.95) = 0.857375
    for b) 1-0.857375-0.000125-(whatever you get in c)
    for c) I would think that it's (0.05)(0.05)(0.95) = 0.002375, but I know that this is incorrect since then solution in the back of the book is 0.007125
    for d) I know it's (0.05)(0.05)(0.05) = 0.000125
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  2. #2
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    This is binomial.

    part c, C(3,2)(.05)^{2}(.95)=.007125
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