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Math Help - Probability - Hypergeometric random variable

  1. #1
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    Probability - Hypergeometric random variable

    I am trying to help my child with her homework, and I don't have a clue how to answer this.

    Four ball are randomly selected without replacement from an urn containing 20 balls numbered 1 - 20

    1.A) Let Y denote the number of balls numbered 16 or higher. Determine the probabilty distribution ( probability mass function) of Y.

    1.B) Use the probabilty mass function to determine the probability that the largest value in the selection is at most 15.

    2.A) Let X equal the largest number in the selection. Is X hypergeometric?
    2.B) Determine the probablity distribution (probability mass function) of X. Use this to determine the probability that the largest value is at most 15.


    I could use any help you can offer on this. Thanks.
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  2. #2
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    Quote Originally Posted by PatCal View Post
    I am trying to help my child with her homework, and I don't have a clue how to answer this.

    Four ball are randomly selected without replacement from an urn containing 20 balls numbered 1 - 20

    1.A) Let Y denote the number of balls numbered 16 or higher. Determine the probabilty distribution ( probability mass function) of Y.

    1.B) Use the probabilty mass function to determine the probability that the largest value in the selection is at most 15.

    2.A) Let X equal the largest number in the selection. Is X hypergeometric?
    2.B) Determine the probablity distribution (probability mass function) of X. Use this to determine the probability that the largest value is at most 15.


    I could use any help you can offer on this. Thanks.
    I will get you started:

    Question 1

    Using the notation found here: Hypergeometric distribution - Wikipedia, the free encyclopedia

    Y ~ Hypergeometric(m = 5, N = 20, n = 4)

    (a) Substitute the above values into the pmf given at the above link. Note that the support of Y (that is, the values that Y can have) is 0, 1, 2, 3, 4.

    (b) The probability that the largest value in the selection is at most 15 will be Pr(Y = 0) (why?).


    Question 1

    (a) No.

    (b) Calculate \Pr(X \leq 15) = 1 - Pr(X > 15).
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  3. #3
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    Probability - hypergeometric

    Thank you for the reply, but I still do not understand.

    PatCal
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  4. #4
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    Quote Originally Posted by PatCal View Post
    Thank you for the reply, but I still do not understand.

    PatCal
    What don't you understand? Please be specific.
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  5. #5
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    Probability - hypergeometric variable

    I am sorry, but I do not understand this question at all. I need to be walked through all the steps.

    It has been 30 years since I did this sort of stuff, and it just isn't sticking .

    PatCal
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  6. #6
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    Quote Originally Posted by PatCal View Post
    I am sorry, but I do not understand this question at all. I need to be walked through all the steps.

    It has been 30 years since I did this sort of stuff, and it just isn't sticking .

    PatCal
    Have you read the link?
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