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leephy (leephy) 于 (Mon Feb 25 17:42:59 2008) 提到:
birthdays of 20 members of a club are assumed to be independently and
uniformly distributed over the twelve months. Let Z be the number of months
during which at least one member has a birthday. Find Var(Z)?
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leephy (leephy) 于 (Mon Feb 25 18:05:50 2008) 提到:
my answer is 12((11/12)^20-(11/12)^40), is it right?
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helmertb
