回复：回复：儿子拿回来的题, 搞不出了, 请大家帮忙

来源: tony_ren 于 2010-07-03 20:25:31 [] [旧帖] [给我悄悄话] 阅读数 : (74 bytes)

It's probability problem. One should use probability formula to solve it.

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