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There are n sets of twins (so in total 2n people) attending a party. Each twin wears an identical hat to his/her twin sibling, and there are n different kinds of hats. Each person gives there hat to the hat clerk at the beginning of a party and at the end of the party they are randomly given a hat back. If x is the random variable denoting the number of people who have their own hats back, what is pr{X=2n} and E(X)

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    By "their own hats", you mean "their own kind of hat"?2012-11-02

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