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标题: 这道概率题好奇怪讶，请大家帮帮忙 [打印本页]

作者: echozhang20 时间: 2008-1-24 20:44 标题: 这道概率题好奇怪讶，请大家帮帮忙

Q2:从条件1和2 都可得出women 的人数大于5 ，因此p<1/2呀，怎么回事呢？

If 2 different representatives are to be selected at random from a group of 10 employees and if p is the probability that both representatives selected will be women, is p > 1/2？

(1)
More than 1/2 of the 10 employees are women.

(2)
The probability that both representatives selected will be men is less than1/10 .

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer: e

作者: ecsniffers 时间: 2008-1-25 06:29

The answer E is correct. From condition2, you can get the number of men<=3. So if the number of women is 7, P can be caculated to 7/15.

作者: echozhang20 时间: 2008-1-25 20:26

But when men<=3, women can be 7, then the probility of two women being selected is comination of 2 from 7=21, the whole probility is combination of 2 from 10=45, then p=21/45, which is also<1/2, so we should still choose d. Am I wrong somewhere?

作者: echozhang20 时间: 2008-1-26 06:35

oh, I get it, women can be 8, then p=28/45, so e. Thanks a lot!!

作者: thumbwings 时间: 2008-1-28 09:43

 E is correct

作者: oliviachens 时间: 2008-1-31 08:51

QUOTE:

以下是引用thumbwings在2008-1-28 9:43:00的发言：
E is correct

why

作者: 开若兰 时间: 2009-5-31 20:57

QUOTE:

以下是引用oliviachens在2008-1-31 8:51:00的发言：

why

当 women 的人数为 6 时，p < 1/2；当 women 的人数为 8 时，p > 1/2。故（1）和（2）加起来都不充分。

作者: BruceNornia 时间: 2009-6-1 07:00

好牛的考古阿....

这个帖子我都没有翻到过

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