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Math Help - 2 finding probability problems

  1. #1
    m58
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    2 finding probability problems

    Hello,

    I've been re-working two problems since yesterday, and have been getting the same (wrong) result every time. Here are the problems:

    The probability that a person in the US has type B+ blood is 9%. Five unrelated people in the US are selected at random.
    a) Find the probability that all 5 have type B+ blood.

    Here, I would convert 9% to .09. Then, .09 * .09 * .09 * .09 * .09 = .000006

    HOWEVER: the answer key says it is .0000059

    b) Find the probability that none of the five types have type B+ blood.

    1 - .000006 = .999994

    then

    .999994 * .999994 * .999994 * .999994 * .999994 = .99997

    HOWEVER:
    the answer key says it is .624

    c) Find the probability that at least one of the five has type B+ blood.

    1 - .99997 = .00003

    HOWEVER: the answer key says it is .376


    The second problem confused me from the get-go. Would you mind giving me a hint on how to start it?
    A distribution center receives shipments of a product from 3 different factories in the following quantities: 50, 35, and 25. Three times a product is selected at random, each time without replacement. Find the probability that:
    a) All three products came from the third factory?
    b) None of the three products came from the third factory?
    Thanks in advance!
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  2. #2
    MHF Contributor

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    Re: 2 finding probability problems

    Quote Originally Posted by m58 View Post
    Hello,

    I've been re-working two problems since yesterday, and have been getting the same (wrong) result every time. Here are the problems:

    The probability that a person in the US has type B+ blood is 9%. Five unrelated people in the US are selected at random.
    a) Find the probability that all 5 have type B+ blood.

    Here, I would convert 9% to .09. Then, .09 * .09 * .09 * .09 * .09 = .000006
    HOWEVER: the answer key says it is .0000059

    b) Find the probability that none of the five types have type B+ blood.

    1 - .000006 = .999994
    then
    .999994 * .999994 * .999994 * .999994 * .999994 = .99997

    HOWEVER:
    the answer key says it is .624
    c) Find the probability that at least one of the five has type B+ blood.
    1 - .99997 = .00003
    HOWEVER: the answer key says it is .376
    (.09)^5=0.0000059049

    (.91)^5=0.6240321451

    1-(.91)^5=0.3759678549
    Thanks from m58
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