回複：回複：兒子拿回來的題, 搞不出了, 請大家幫忙

來源: tony_ren 於 2010-07-03 20:25:31 [] [舊帖] [給我悄悄話] 閱讀數 : (74 bytes)

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

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