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Math Help - probability

  1. #1
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    Question probability

    please help me i hate probabilty!

    Two students Alan and Brenda are due to take an examination. The probability that Alan will pass is 3/5 the probability that Brenda will fail is 4/7.

    a) calculate the probability that both will fail

    b) calculate the probability that only one will pass

    c) if Brenda fails the probability that she will pass next time is 2/5

    (i) calculate the probability that Brenda fails again
    (ii) calculate the probability that Brenda passes having taken the examination for a second time
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by si55ler View Post
    please help me i hate probabilty!

    Two students Alan and Brenda are due to take an examination. The probability that Alan will pass is 3/5 the probability that Brenda will fail is 4/7.

    a) calculate the probability that both will fail
    That A and B pass/fail are independent events so the probability that
    they both fail:

    P(A fails and B fails)=P(A fails) P(B fails) = (1-3/5) x 4/7 = 8/35


    b) calculate the probability that only one will pass
    P(only one will pass) =P(A pass and B fails) + P(A fails and B pass)=(3/5)x(4/7) + (2/5)x(3/7)=...

    c) if Brenda fails the probability that she will pass next time is 2/5

    (i) calculate the probability that Brenda fails again
    This is a bit vaguely worded, but given that B has failed the probability that she
    fails the second time is 1 minus the probability that she passes the second time = 3/5.


    (ii) calculate the probability that Brenda passes having taken the examination for a second time
    The wording of this is even more ambiguous, the best I can make of what is asked is 2/5,
    but I don't think that is what is intended.


    RonL
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