问一个数学问题，请大家帮忙，为了孩子考试 donz940862007-01-24 04:59:13

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

doesn't A,B,C,D,E make 5 possible answers?

I read it twice, I cant understand it. Can u tanslate into

这是原题么？还是翻译的版本?

这是原题，一字不错， 是中学 几何和离散数学课本中的一题