[問題] 問一個期望值的問題
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?
想了很久...試過很多種想法算出來都不對= ="
請教板上的高手了
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