我是这样想 问说有六个字母:A B B C C C 可以怎排列 看你要先看三组中的哪组 假设就照A B C的顺序 A有六个空间让他排 所以是6种 B B有剩下的五个空间让他们排 所以是C5取2 C C C有三个空间让他们排 其实也只能有一种排法了 要写成C3取3或直接写成1都可 三组相乘 所以共60种方法 你要从B或C开始排也可 答案会一样 ※ 引述《RainySunDay (Heart fly)》之铭言： : 1.How many different 6-letter sequences are there that consist of 1 A, 2 B's, : and 3 C's? : A:60 : 2.Apharmaceutical company received $3million in royalties on the firs $20 : million in sales of the generic equivalent of one of its products and then : $9million in royalties on the next $108 million in saes. By approximately : what percent did the ratio of royalties to sales decrease from the first $20 : million in sales to the next $108 million in sales? : A:45% : ps. The first question is I have a gap in memory of permutation formula : The second question is I am a little bit confused with its meaning. : Is the following equation right? [3/20-9/108]/ 9/108=87.5% : Thanks for your patience. -- No doubt, just keep walking --

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