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    I need some help at the following exercise...
    We have a container that contains r balls that have numbers 1,...,r. We choose at random n of them without replacement. Let Y be the greatest and Z the smallest of the numbers of the balls we chose. Which are the probabilities P(Y<=y) and P(Z>=z)???

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    (Original post by mathmari)
    I need some help at the following exercise...
    We have a container that contains r balls that have numbers 1,...,r. We choose at random n of them without replacement. Let Y be the greatest and Z the smallest of the numbers of the balls we chose. Which are the probabilities P(Y<=y) and P(Z>=z)???

    Considering your first one, P(Y<=y).

    Since Y is the greatest no. of the balls chosen. This can be paraphrased as "What is the probability that all n balls chosen are less than or equal to y".

    Is that sufficient for you to complete it?

    Edit: Corrected - had strict inequalities, when it should have been <=.
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    Is that {y choose n}/{r choose n}???????
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    (Original post by mathmari)
    Is that {y choose n}/{r choose n}???????
    You got it.
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    And how can I find the possibility P(Z>=z)???
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    (Original post by mathmari)
    And how can I find the possibility P(Z>=z)???
    Look back at how you did Y and have a think at how you could adapt the throught process for this situation, and the definition of Z.
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    Ok...Thank you very much!!!
 
 
 
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