再问费费第六部分1（happyfish看过来）

hitlzc

以下是引用slickwx在2006-7-12 15:00:00的发言：

hitlzc,

我对你的解答中有一部分不太确定:

P（A非|B非）=P（A非*B非）/P（B非）

=》 P（B非）=P（A非|B非）/P（A非*B非）=3%/60%=5%

=》P（B）=1-P（B非）=95%

为什么P (B)=1-P(B非), 根据你的定义:

B代表事件the policies having correct  electric record

B非：代表the policies having incorrect electric  record

所以P(B)+P(B非)是等于所有有电子记录的POLICIES. 而所有有电子记录的POLICIES的概率不为1,因为还有只有PAPER记录的POLICIES存在.

请指教.谢谢

您提的问题非常好，谢谢，这是我之前没有考虑到的地方。

我又想了一下，认为下面说明比较准确

请参见：http://forum.chasedream.com/dispbbs.asp?boardid=22&replyid=609122&id=4937&page=1&skin=0&Star=5

以下是引用耳朵在2004-2-10 3:16:00的发言： 第一题，题目第一句话说的是：“each policy has a paper record or an electric record”，就是两者只居其一即可，有只有P的也有只有E的，也有两个都有的。但是问的是P和E都正确的概率。可是不知道P和E单独的比例，因此这个算法不完整。

以下是引用耳朵在2004-2-10 3:49:00的发言： （见32楼）画了个图，表示得更清楚。题目中要求的是黄色的部分，即B。已知A+B+C+D+E+F=1，而现在E等于（D+E）的60%，也等于（E+F）的75%，但是算不出来A和C，所以B占的比例无法求出。

以下是引用bunnier在2004-6-20 0:06:00的发言：

Once again, if the answer must be right, then its question must be wrong... for the record: 94% is the right answer for the following questions:

• what is the probability that a policy isn't recorded incorrectly? (~P & ~E)
• what is the probability that it is one having correct paper [or] correct electric record, [or both]? (P | E)

As for the question "what is the probability that it is one having both correct paper and correct electric record?" (P & E), agree with 耳朵gg that the problem doesn't offer enough information to solve it. However, if the problem states that each policy has a paper record and an electric record, the question is solvable... a revised #1:

In an insurance company, each policy has a paper record and an electric record. 60 percent of the policies having incorrect paper record have incorrect electric record and 75 percent of the policies having incorrect electric record have incorrect paper record. 3 percent of all the policies have both incorrect paper and incorrect electric records. If we randomly pick out one policy, what is the probability that it is one having both correct paper and correct electric record?

偶也是这样想的，偶同意耳朵和bunnier的结论和分析！

严重感谢耳朵和bunnier！！！

建议版主在方便的时候可以在费费详解版里注明一下此题目本身有争议，请大家进入论坛看具体讨论。这样后来的XDJM可以看到完整的分析哦。

slickwx

晕..呵呵.这样改题目的确就没有问题了....

请教HITLZC类似德.摩根定律的公式还有哪些,,呵呵,已经离开学校多年,都不知道该去哪本书找这样的公式. 如果方便的话,希望您能归纳一下. 这类的题目在GMAT里面多吗?

非常感激你们的工作.

hitlzc

以下是引用slickwx在2006-7-12 16:04:00的发言：

晕..呵呵.这样改题目的确就没有问题了....

请教HITLZC类似德.摩根定律的公式还有哪些,,呵呵,已经离开学校多年,都不知道该去哪本书找这样的公式. 如果方便的话,希望您能归纳一下. 这类的题目在GMAT里面多吗?

非常感激你们的工作.

应该说类似的题目在一套题，37道里面出现的机会很小，我觉得顶多1-2道，或者没有。

从复习时间的角度看，没必要重点复习。我觉得一般只要多看JJ,了解思路即可。

 

 下面是概率论的一些基本概念，在涉及到相关题目时可以查阅参考一下。

挥着猪翅膀

以下是引用hitlzc在2006-6-13 15:38:00的发言：

我认为此题是条件概率问题：

1.In an insurance company, each policy has a paper record or an electric record, or both of them. 60 percent of the policies having incorrect paper record have incorrect electric record and 75 percent of the policies having incorrect electric record have incorrect paper record. 3 percent of all the policies have both incorrect paper and incorrect electric records. If we randomly pick out one policy, what is the probability that it is one having both correct paper and correct electric record?
Answer:94%

设A代表事件the policies having correct paper record

B代表事件the policies having correct  electric record

A非：代表the policies having incorrect paper record

B非：代表the policies having incorrect electric  record

（1）所以根据题目：

60 percent of the policies having incorrect paper record have incorrect electric record

可以写成P（A非|B非）=60%

75 percent of the policies having incorrect electric record have incorrect paper record.

可以写成P（B非|A非）=75%

3 percent of all the policies have both incorrect paper and incorrect electric records.

可以写成P（A非*B非）=75%（此处*代表交集的意思）

（2）根据条件概率的定义有

P（A非|B非）=P（A非*B非）/P（B非）

=》 P（B非）=P（A非|B非）/P（A非*B非）=3%/60%=5%

=》P（B）=1-P（B非）=95%

P（B非|A非）=P（A非*B非）/P（A非）

=》 P（A非）=P（B非|A非）/P（A非*B非）=3%/75%=4%

=》P（A）=1-P（A非）=96%

（3）要求P（AB）=？

根据[upload=jpg]UploadFile/2006-6/200661315324463328.jpg[/upload]

所以[upload=jpg]UploadFile/2006-6/200661315344495800.jpg[/upload]
=》P（AB）=P(A)+P(B)+P（A非*B非）-1=96%+95%+3%-1=94%

  不要把那些逻辑抗过来，GMAT是它独有的CR，你拿普通逻辑学那一套来是白费力。

yaoyao99

啊哈哈，普通逻辑是基础，还是有用。

bluegold998

如果题目是原来的，那确实没办法解。

slickwx

以下是引用hitlzc在2006-7-12 18:04:00的发言：

应该说类似的题目在一套题，37道里面出现的机会很小，我觉得顶多1-2道，或者没有。

从复习时间的角度看，没必要重点复习。我觉得一般只要多看JJ,了解思路即可。

 

 下面是概率论的一些基本概念，在涉及到相关题目时可以查阅参考一下。

感谢分享.

fengfengok

agree with slickwx. so what is the answer.

wotaowoyao

救命啊这题我连题目意思都看不明白,怎么办?跪求翻译!

carp

同感。还好看见大家的帖子，否则还以为自己想错了。

应该是题目的问题，个人觉得把问题改成what is the probability that it is one having correct paper [or] correct electric record? 这样就把剩下的全含该进去了。