确认一下gwd23－30的答案

长滩 · 发表于 2009-8-7 00:59:00

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?

40
45
50
55
60
我算出来是55，可答案是50

budexing2 · 发表于 2009-8-7 03:25:00

c84-c64

长滩 · 发表于 2009-8-7 10:07:00

我算出来是55，可是答案是50。是不是答案不对？

确认一下gwd23－30的答案

确认一下gwd23－30的答案

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