given a collection of 2n objects,n of which are identical and n of which are all distinct,how
many different subcollection of n objects are possible?有一系列2N的东西 N个事一样的 N个事不一样的 有多少个集合？ 答案是NC0＋ Nc1 + ......+Ncn
人气：306 ℃ 时间：2020-05-10 13:54:20
解答
如果该集合中只有一个,那么就有N+1个集合,如果有两个,则有两种1是在n个一样的中选一个和不一样的中选一个,则有n中,2,就是两个全是不一样的,就只有在那N个不一样的东西中选择,就有C20,2,如果有三个,也有两种,一是在不一样中的选择两个,一样的一个,就有C20,2种,第二就是全在不一样事物中选择3个,就有C20,3种,以此类推,就会得到答案的、谢谢,
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