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
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我去～～我竟然看成了求概率，题目就是要求几种可能性，没有要求概率！！！
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我去～～我竟然看成了求概率，题目就是要求几种可能性，没有要求概率！！！
登录 或 注册 后可以参加讨论