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题目内容
There are 10 books on a shelf, of which 4 are paperbacks and 6 are hardbacks. How many possible selections of 5 books from the shelf contain at least one paperback and at least one hardback?
A、75
B、120
C、210
D、246
E、252
答案:D
专业教师答疑
问题:为什么c(4,1)c(6,1)c(8,3)取出来的是不完整的
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问题:请问数学老师,为什么不是绿色笔写的那种。我四本paperback选一本,六本hardbacks选一本,接下来我随便选嘛。
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