GWD23-Q30

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?

A.     
40

B.      
45

C.     
50

D.     
55

E.      
60

 答案是c，我算了n次都是d。。。C(1,2)C(3,6) + C(2,2)C(2,6)   注：C(1,2)指的是组合，1在上面，2在下面，这样想的，为啥米不对呐？还是我计算有问题？？

应该是答案错了吧