回複：回複：依次任取7個小於等於10的正整數，求其和為20的概率？

來源: 於 2010-06-07 10:01:11 [舊帖] [給我悄悄話] 本文已被閱讀：次

agree- seems to be a 體力活 to me too. did not a see shortcut solution.

my estimated result is about~ 0.3%.