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标题: [求助]急问答案及解题过程，烦劳XDJM们帮忙 [打印本页]

作者: lori 时间: 2005-11-19 10:42
标题: [求助]急问答案及解题过程，烦劳XDJM们帮忙

Q6:

A box contains 10 light bulbs, fewer than half of which are defective. Two bulbs are to be drawn simultaneously from the box. If n of the bulbs in box are defective, what is the value of n?

(1) The probability that the two bulbs to be drawn will be defective is 1/15.

(2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.

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.

另外能否指点一下想这累的概率题目应该如何入手，我现在碰到这种题目就害怕，心一凉就怎么都不会了，应该怎么办？还有三天考试，还有办法跨越这个障碍吗？

作者: 加拿大帅哥 时间: 2005-11-19 11:56

你先不要急，有时候如果看不出来就先放在那里。第二天再看，反而自己就会了。

思路好像应该是这样：用组合公式

1。C(n,2) /C(10,2) =1/15 得出C(n,2)=3 则根据经验和常识 n=3

2. C(n,1) * C(10-n,1) /C(10,2) =7/15, 得出 n = 3 or 7, 根据条件可否定7

Therefore, the answer is : D

作者: lori 时间: 2005-11-19 13:24
谢谢你的解答，更谢谢你的建议，谢谢。你说得对，只是一看是概率心里就毛了，就似乎怎么也不会了，其实应该克服一下的，谢谢你！

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