问一个数学问题，请大家帮忙，为了孩子考试

来源: donz94086 于 2007-01-23 20:59:13 [] [旧帖] [给我悄悄话] 阅读数 : (281 bytes)

You are given a collection of 20 multiple choice questions, four each possible answers A, B, C, D, or E. How many different sets of ten questions can be formed if the set has exactly two questions with each possible answer?
answer is 7776, but dont know to how get it
thanks

所有跟帖： 

• doesn't A,B,C,D,E make 5 possible answers? -DaBoys- ♂ 给 DaBoys 发送悄悄话 (0 bytes) () 01/23/2007 postreply 22:07:50

• I read it twice, I cant understand it. Can u tanslate into -SunOfBeach- ♂ 给 SunOfBeach 发送悄悄话 (8 bytes) () 01/24/2007 postreply 07:49:28

• 这是原题么？还是翻译的版本? -我稀饭捣乱- ♀ 给 我稀饭捣乱 发送悄悄话 (293 bytes) () 01/24/2007 postreply 08:22:23

• 这是原题，一字不错， 是中学 几何和离散数学课本中的一题 -donz94086- ♂ 给 donz94086 发送悄悄话 (20 bytes) () 01/24/2007 postreply 17:19:54

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