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Thread: Average number, combinatorics

  1. #1
    Junior Member
    Nov 2012

    Average number, combinatorics

    Please help me solve these problems.

    1. Nine boys and fourteen girls are arranged in a row in all possible ways. What is the average number of "neighbours" of opposite sex.

    2. Consider a family of all $\displaystyle k$-element subsets of a set $\displaystyle \left\{ 1,2,......,2n\right\}$. For every such set consider its smallest element. Find the average value of the smallest element in all $\displaystyle k$-element subsets.
    Last edited by wilhelm; Nov 30th 2012 at 05:31 AM.
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