問一個數學問題，請大家幫忙，為了孩子考試

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- ♂ (0 bytes) () 01/23/2007 postreply 22:07:50

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

• 這是原題麽？還是翻譯的版本? -我稀飯搗亂- ♀ (293 bytes) () 01/24/2007 postreply 08:22:23

• 這是原題，一字不錯， 是中學 幾何和離散數學課本中的一題 -donz94086- ♂ (20 bytes) () 01/24/2007 postreply 17:19:54