Math

Twenty tires are tested to see if they last as long as the manufacturer claims they do. Three tires fail the test. Two tires are selected at random without replacement for an inspection.
Find the probability that both tires fail the test.
Which is greater, the probability that the first tire fails and the second one passes? or vice-versa?

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asked by Steve
  1. p(f) = 3/20

    p(first) = 3/20 = .15
    p(second) = 2/19 = .105

    p first and second = .15 * .105 = .0158

    first fail, second pass
    = 3/20 * 18/19

    first pass second fail = 17/20 * 3/19

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    posted by Damon

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