[問題] Please help a "vegetable bird" like me

[RainySunDay (Heart fly)]

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.

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推 flac:1. 6(C5取2)(C3取3)  2.[3/20-9/108]/(3/20)=0.446
推 thdkuo:能不能請flac大解釋一下1的算法啊 @@?
推 flac:補充一下 用rookie會比vegetable bird好 哈
→ RainySunDay:謝謝flac。