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There are 10 different books available to a librarian for purchase, each for the same price, but the librarian has only enough money to purchase 9 of them. How many different collections of 9 books are there that can be selected from the 10 books?
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· 相关考点
6.3.5 组合
6.3.5 组合
以上解析由 考满分老师提供。
