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标题: 有十个球，一个绿，一个蓝 [打印本页]

作者: renali 时间: 2002-12-24 08:08 标题: 有十个球，一个绿，一个蓝

1.，有十个球，一个绿，一个蓝依次取三个球不放回，求第一个是绿，其它二个不是蓝的概率
-答案：确认： 7/30
思路： /

Who can tell me how to get the ans.7/30?

作者: lisaislisa 时间: 2002-12-24 09:15

C2,8/C3,10

^^

作者: renali 时间: 2002-12-24 11:43

Lisaislisa:

Can you explain to me the meaning of C2,8?

作者: xiaoyayah 时间: 2002-12-24 12:39

I think that it should be 7/60

作者: xiaoyayah 时间: 2002-12-24 13:31

sorry,there is more reasonable explaination

8*7)/(10*9*8)=7/90
attention:take out one by one

作者: renali 时间: 2002-12-24 14:02

Xiaoyayah

I agree with you. the ans.should be 7/90

作者: lisaislisa 时间: 2002-12-24 14:50

C2,8 means after taken one green ball ,
the different other alternatives that may occur as I choose the other two balls
since I can not get the blue one
it should be 8...
get what I mean ?

^^
Merry X'mas to all !

作者: renali 时间: 2002-12-25 01:03

I finally got it. Thanks

Merry Christmas and Happy new year to you all

作者: xiaoyayah 时间: 2002-12-25 13:14

take out the green one:the probility is 1/10, so the ans. must be less than 1/10.

作者: renali 时间: 2002-12-26 05:11

xiaoyayah:
That's what I think: take out the green one:the probility is 1/10. then cannot take the blue one possibility is 1-1/9, same to 1-1/8
=> 1/10*(1-1/9)*(1-1/8)=7/90

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