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Math Help - Help:calculate the expectation

  1. #1
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    Question Help:calculate the expectation

    k obeys hypergeometric distribution. Every time, I pick up k balls from the population N balls, which have m red balls. I want only one red ball in each pickup event.
    Here is my question, how can I calculate the expectation of k.

    E(k)=\sum_{k=1}^{N-m}\frac{(^m_1)(^{N-m}_{k-1})}{(^N_k)}k=?

    very thank for your help.
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  2. #2
    MHF Contributor
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    If you rewrite the coeficients as factorials, it may become more obvious.

    Maybe not. Try exploring a little.
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