Sunday, 25 August 2013

Probability of n balls in n cells, one remaining empty

Probability of n balls in n cells, one remaining empty

Counting problems have always intrigued me, and I'm working on some out of
interest. The other thread on this topic had unsatisfactory answers,
because they don't match the answer in my book.
My question is: If n balls are placed at random into n cells, find the
probability that exactly one cell remains empty.
My book gives (n choose 2) * n!/n^n.
But I'm not sure which answer is right?

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