【GMAT数学易错点总结】韦恩图的小秘密

鹰击长空94

A lot of the information in the table just serves as a distraction here. The first column of the table gives us a standard 2-circle Venn diagram: those people who like M, those people who like N, and those people who like both. We want to know how many like both. If we know exactly how many people are in our diagram (i.e. how many people responded 'favourable' to at least one candidate), we can answer that question. Statement 1 tells us that 40 of the 100 people are *not* in our diagram, so 60 people must be in the diagram, and that info is sufficient. I can't draw a Venn diagram here, but I'd fill it in as follows:

Favorable for M only: 40 - x
Favorable for both M and N: x
Favorable for N only: 30 - x

From Statement 1 I know these three quantities add to 60, which gives me one equation in one unknown.

Statement 2 doesn't tell you how many people are in the diagram, so is not sufficient.

As for your question about using a 'matrix' or 'formula' here, I wouldn't consider doing either.       

注：引用gmatclub的解释，感觉更清晰直观，且答案应该是10？

秋风

真的要给你一朵小花花！！！

Kaceykeke

lulusea

biubiubiu盖盖

Mark一下！               

bluesky0406

感谢楼主！
指出一个错误：例题1-3。
Step1正确，但Step2中应改为：
NF总共90人，取补集——剩下那10个就是双方都支持的。
正确答案是10人。

1234rr

1-3怕是错了哦。
(1) The number of voters who did not respond “favorable” for either candidate was 40.
根据条件1的表述，可知没给任何一个候选人投favorable的是40人，这些人可能同时给M和N投了Unfavorable，也可能同时给M和N投了 Not Sure。或者给M投了Unfavorable给N投了 Not Sure。反正是这些人加起来就是40个。这样的话，给M和N投了favorable的就是60人，有只给M投的，有只给N投的，有同时给M和N投的。表格中favorable那一栏总人数是70人，其中包含了同时投了两个人favorable的选票。设这个重复的选票数为x，则40+30-x=60.得出x等于10. 所以A是充分的。
(2) The number of voters who responded “unfavorable” for both candidates was 10.
很明显，经过上面的分析，只知道同时给M和N投了unfavorable的人是10个，也仅仅能够知道给M和N投票的人一共是45.不知道别的信息的基础上，是得不出同时给M和N投favorable选票的人数的。

Kic

Mark一下！               

玻璃心的大女王

谢谢整理君！真是及时雨啊！太棒了

我是Elsa

秒速N光年 发表于 2017-9-23 01:04
感谢分享！

感谢解答