作者gwish (暧暧内含光)
看板Statistics
标题[问题] nb的问题
时间Tue Dec 5 23:13:10 2006
One of four different prizes was randomly put into each box of a cereal.
If a family decided to buy this cereal until it obtained at least one of
each of the four different prizes,what is the expected number of boxes
of cereal that must be purchased?
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