国际顶尖MBA申请交流平台--TOPWAY MBA

标题: 请问Prep一道组合题 [打印本页]

作者: Cherliuiking 时间: 2013-1-22 07:03 标题: 请问Prep一道组合题

66. From a group of 21 astronauts that includes 12 people with previous experience in space flight, a 3-person crew is to be selected so that exactly 1 person in the crew has previous experience in space flight. How many different crews of this type are possible?

(A) 432

C1^12 C2^9 和C1^12*2C1^9是一个意思么？
如果是，具体怎么展开？我怎么算不出432呀？

请nn指正！多谢！

作者: baochangzx 时间: 2013-1-22 20:31

先从12个有经验的人中选择一个，从剩下9个没有经验的人当中选择2个，

(12*9*8)/2=432

作者: Cherliuiking 时间: 2013-1-23 06:42

为什么要除以2呀？

作者: Cherliuiking 时间: 2013-1-23 06:42

啊，懂了！多谢!

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