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There will be 5 songs and 3 dances in a performance. How many distinguished way to arrange the shows if all dances cannot be next to each other? (1) How many distinguished ways to arrange the shows? (2) How many distinguished ways to arrange the shows if all dances must be next to each other? (3) How many distinguished ways to arrange the shows if all dances cannot be next to each other? 答案： （1）p(8,8) = 8! （2）p(6,6) * p(3,3) = 6!*3! （3）p(8,8) —p(6,6) * p(3,3). 第三题为何是用全部情况减去dances must be next to each other的情况？ 这样得到的结果难道不是包括了"有两个dances是next to each other，而另外一个dance没有"的情况吗？ | 
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发表于 2016-8-19 13:19:10
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