在看看这题难道我的答案都有问题？？？

sunflowerstar

Q30:

There are 8 books on a shelf, of which 2
are paperbacks and 6 are hardbacks.  How
many possible selections of 4 books from this self include at least one
paperback?

怎么算都是55种，怎么答案是50种呢？？？

melissasun

偶也算的55

可能是1本或2本paperback。

2*C(3,6)+C(2,6)=55

hitlzc

同上

sunflowerstar

唉，看来不能尽信答案的。