[推荐]GMAT逻辑问题 NN回答部分精华

myice

逻辑区的一些东西，我看了很有启发，拿来大家一起看，算是向NN致敬，同时谢谢小安GG的提醒。

1.    Efficiency and redundancy are contradictory characteristics of linguistic systems: however, they can be used together to achieve usefulness and reliability in communication. If a spoken language is completely efficient, then every possible permutation of its basic language sounds can be an understandable word. However, if the human auditory system is an imperfect receptor of sounds, then it is not true that every possible permutation of a spoken language’s basic language sounds can be an understandable word.
If all of the statements above are true, which one of the following must also be true?
(A) Efficiency causes a spoken language to be useful and redundancy causes it to be reliable.
(B) Neither efficiency nor redundancy can be completely achieved in spoken language.
(C) If a spoken language were completely redundant, then it could not be useful.
(D) If the human auditory system were a perfect receptor of sounds, then every permutation of language sounds would be an understandable word.
(E) If the human auditory system is an imperfect receptor of sounds, then a spoken language cannot be completely efficient.
3. 我认为先用排除法. 这种题目要把思路严格地局限在原文的逻辑关系内, 当自己是个idiot.
原文中的两个IF标出了逻辑关系:
1. "a spoken language is completely efficient"(A)-->"every possible permutation of its basic language sounds can be an understandable word"(B);
2. "the human auditory system is an imperfect receptor of sounds"(C)-->"it is not true that every possible permutation of a spoken language’s basic language sounds can be an understandable word"(非B)
然后看选项:
A. 不对, 原文没有提到这两个逻辑关系
B. 不对, 原文没有提到complete redundancy可能性. 原文提到了complete efficiency, 但是并没有说它是否可能. 从原文的第二个逻辑关系看, 如果听觉系统不完善, complete efficiency才不可能, 言下之意是如果听觉系统完善(即使这个假设是错的, 原文并没有否定这个假设, 所以不违背原文的逻辑关系),就可以达到complete efficiency.
C. 不对, 原文没有提到complete redundancy
D. 不对, 此选项是第二个逻辑关系的否命题, 与原命题不等价,可对可错, 不能从原文推出来.
E. 对. C-->非B-->非A
你可以通过相关性排除前三个选项, 再根据逻辑关系找出D的错误并验证E的正确性.
1. 所谓其它原因削弱是指用一个新的原因解释现象, 答案中一定会将新的原因和现象联系起来. 你回想一下以前所见过的题目, 新的原因不会是单独给出不和现象联系. 例如那道孵蛋的问题, 新的原因说蛋的质量随时间变化, 和孵蛋有关. 举一个假设题目中的非它因: 杜德伟吃多了,杜德伟肚子痛,所以吃多了-->肚子痛. assumption就是不是因为吃了E coli而导致了肚子痛. 如果选项只说他没吃E coli, 就不是答案, 因为没有将E coli和肚子痛联系在一起, 并且common sense也不能解释.
Heat在原文中并没有提到, 你不能确认是否观测到了heat, 所以无关.

myice

14. Among the more effective kinds of publicity that publishers can get for a new book is to have excerpts of it published in a high-circulation magazine soon before the book is published. The benefits of such excerption include not only a sure increase in sales but also a fee paid by the magazine to the book's publisher.

Which of the following conclusions is best supported by the information above?
(A) The number of people for whom seeing an excerpt of a book in a magazine provides an adequate substitute for reading the whole book is smaller than the number for whom the excerpt stimulates a desire to read the book.

(B) Because the financial advantage of excerpting a new book in a magazine usually accrues to the book's publisher, magazine editors are unwilling to publish excerpts from new books.

(C) In calculating the total number of copies that a book  has sold, publishers include sales of copies of magazines that featured an excerpt of the book.

(D) The effectiveness of having excerpts of a book published in a magazine, measured in terms of increased sales of a book, is proportional to the circulation of the magazine in which the excerpts are published.

(E) Books that are suitable for excerpting in high-circulation magazines sell more copies than books that are not suitable for excerpting.
答案：A
这是一道很好的例题. 它的选项有迷惑性在于不止一个选项读上去是正确答案. 实际上, 根据所问问题, A,B,D,E都可能是正确答案. 这也是我认为做CR不能单凭直觉的原因. 因为平时做了很多真题, 看了很多答案, 如果不认真理解对错的原因, 而是凭对正确答案的"脸熟", 此题很可能误选.
此题关键在于问题. 是结论或推论.

首先认真读题: 第一句(A), 可能是结论, 说在high-circulation的杂志上excerpting soon before publishing有效; 第二句是premises: increased sales (B1)和fees paid by M (B2). 所牵涉的事物: books, soon before it is published, high-circulation Mag, icreased sales, fees.

推论题(inference)一般可以用取非来做. 即取非后原结论不成立. A为答案. A的意思是读完摘录的人中, 更想买此书的人数要大与看了摘录就不想买此书的人.取非后, B1不成立, 则结论错.

下面我解释一下其它选项:
B看上去是削弱题(weakean, cast doubt)答案. 但我认为不是. 这正体现了ETS的tricky. 由B本身不能反驳原文的逻辑关系A-->B1 and B2. 既, 即使杂志不情愿刊登, 此逻辑关系依然hold. 如果把原题改动一下, 结论变为:A-->在杂志上刊登摘录是一种很popular的方法, 则Bweaken. 因为杂志不愿意刊登, 所以popular的可能性小.

D是support题型的答案. 和A一样, 含有数学概念, 也极象正确答案. 但是我在以前的回复中讲过, 数学概念稍微复杂一些, A是很绝对的比较,N>M, 而D是间接的比较N=rM. 如果此等式不成立(取非),原结论成立吗? 当然. 如果N=M+p, 结论一样成立. 所以不是inference
E也象正确答案, 但是它是weaken结论:所有书在杂志上excerpt后都卖得一样好. 和原文无关.

还有，做ＣＲ时不要跳跃式阅读，要抓住每个关键的名词，动词，形容词和副词．比如此题中的状语soon before it is published完全可以据此出一题：weaken 答案：人们在临近书发行时看到excerpt就不想买了．
我的建议是:读懂文章，找到相关事物，分析选项．

myice

10. Millions of irreplaceable exhibits in natural history museums are currently allowed to decay. Yet without analyses of eggs from museums, the studies linking pesticides with the decline of Birds of prey would have been impossible Therefore, funds must be raised to preserve at least Those exhibits that will be most valuable to science in the future
The argument presupposes that:
(A) If a museum exhibit is irreplaceable, its preservation is of an importance that overrides economic considerations.
(B) The scientific analysis of museum exhibits can be performed in nondestructive way
(C) Eggs of extinct species should be analyzed to increase knowledge of genetic relationships among species
(D) It can be known at this time what data will be of most use to scientific investigators in the future
(E) The decay of organic material in natural history exhibits is natural and cannot be prevented
答案：D，不明白D为什么是假设。
2. 原文说我们一定要做XXXXX, 其中一个假设就是XXXXX is doable. 这里就是我们可以知道哪些是最有价值的. 同理, 假设还可以是: we can possibly raise some或是the decay can be prevented.
此题的迷惑选项教多:
A. 错, 因为没有讨论economic consideration. 如果原文提到没有钱或经济不允许, 此选项才可能对
B. 错, 无关, 因为原文未提到要在实验中保护标本. 如果提到要永久地保护标本, 就对
C. 错, 无关, genetic relation不在原文讨论范围内
E. 错, 与原文想反.

myice

1. Cable-television spokesperson: Subscriptions to cable television are a bargain in comparison to "free" television. Remember that "free" televi-sion is not really free. It is consumers, in the end, who pay for the costly advertising that supports "free" television.

Which of the following, if true, is most damaging to the position of the cable-television spokesperson?

(A) Consumers who do not own television sets are less likely to be influenced in their purchasing decisions by television advertising than are consumers who own television sets.

(B) Subscriptions to cable television include access to some public-television channels, which do not accept advertising.

(C) For locations with poor television reception, cable television provides picture quality superior to that provided by free television.

(D) There is as much advertising on many cable-television channels as there is on "free" tele-vision channels.

(E) Cable-television subscribers can choose which channels they wish to receive, and the fees vary accordingly.

答案：D，我不明白D为什么是削弱？A: 我试试把我的解题思路讲一讲.
1. 读问题, 知道是weaken类型. 并且是weaken cable provider (因为有时原文有两种意见,所以要清楚是weaken哪个观点或理论).
读原文. 第一句(A), 读完知道是应该是一个结论. 有时会有两个以上的结论, 分为sub-conclusion和conclusion. sub-cobclusion都应该服务于final conclusion. Premises和assumption可以分别支持sub-conclusion和conclusion. (我说得很啰唆, 在做题是一般不用去区分sub和final, 读懂题自然就知道了)
读完第二句 (B), 知道这也是一个conclusion, 或是sub-conclusion. 意思上明显是支持第一句.
读完第三句 (C), 知道是一个premise, 支持第二句.
这样, 读完原文就知道其逻辑推理过程: consumers pay for advertising (C) --> free TV not cheap (B) --> cable is a bargain (A). 还要知道所牵涉的事物: advertising, TV, cable, COST

weaken题型有很多类型, 可以否定原文的依据, 如:没有或有不多advertising, 或advertising已经不costly, 或者不是consumers pay for advertising. 这种题都是直接针对premises, 否认其真实性或可靠性, 其它的例子还有否定问卷调查的结果 by questioning the objectivity or representativeness of the survey.

还有一种类型是否定原文的assumption. 例如此题. 如果问题是cable provider的assumption是什么, 答案是? 就是D的一部分: cable service没有同类的consumers要pay for的advertising. 如果这个assumption(必要条件)不成立, 原文结论不成立.
同理, 此题答案也可以是cable service的某一特点约等于free TV的advertising. 也是否定assumption.

myice

5. Most parents who are generous are good parents, but some self-centered parents are also good parents. Yet all good parents share one characteristic; they are good listeners.
If all of the statements in the passage are true, which one of the following must also be true?
(A) All parents who are good listeners are good parents.
(B) Some parents who are good listeners are not good parent.
(C) Most parents who are good listeners are generous.
(D) Some parents who are good listeners are self-centered
(E) Fewer self-centered parents than generous parents are good listeners
答案：D， 这种some, most, all题怎么做？有什么思路吗？
A: 1. 这类题目首先要把题目读清楚, 并将思路局限在题目中所给的关系内.  
Must be true的题目一般可以正推出来, 因为如果一定对的话, 原文必须给出一个真命题, 还有一个方法就是举反例, 原文没有限制的都可能. 比如说最后一句:all good parents share one characteristic; they are good listeners. 这句话中的关系就是:只要是good parents--->good listeners. 其逆否为等价命题,可以得到:not good listeners-->not good parents.
这里可能正确也可能错的是:good listeners都是good parents;不是good parents-->not good listeners.  此二命题分别是逆命题和否命题, 即可能对也可能错. 因为原文没有对此二命题有限制, 两种情况都可能. 我建议在读题时不要考虑这些引申命题, 在读选项时要考虑.
A. 错, 逆命题, 可错, 如逆命题错, 不成立
B. 错, 逆命题, 可对, 如逆命题对, 不成立
C. 错, most错, 原文没有给出两者关系
E. 错, 原文没有给出两者关系
Some表示有一些, 可以是一个. most表示多数, 要大于50%. 读题是要注意原文所给的范围. 可以画图联系. 这类题我一般用排除和正推直接做.

myice

3. All those who keep a journal will be heard by the next generation. Some of these journal writers are true artists, others humorous observers of the commonplace, and still others insufferable egotists who feel compelled to record their every thought.
If the statements above are true, which one of the following must be true?
(A) Not all of those who are humorous observers of the commonplace will be heard by the next generation.
(B) Everyone who will be heard by the next generation keeps a journal.
(C) The next generation will hear both insufferable egotists and true artists.
(D) Some of those who keep journals are not true artists, humorous observers of the commonplace, or insufferable egotists.
(E) The next generation will bear some of those who are true artists but not all of them.
答案：C，这种　If the statements above are true, which one of the following must be true?题，我有做有错，有什么好办法吗？
谢谢。
3.是不是用举反例的方法可以. 这类题目中经常涉及范围.
A, 你要想:如果all humorous observers of the commonplace都记日志, A就对.所以A可对可错.
B.你要想记日志-->will be heard, 记日志只是一个充分条件, 其它事也可以导致will be heard, 所以可对可错.
C.对.两种人都有记日志的, 而记日志一定导致will be heard, 可以正推出来.
D.和原文相反.
E.如果true artists都记日志,那么E就错.
只要你所想的反例不违背原文的意思, 无论多absurd,都可以用.

myice

4. Handwriting analysis—also known as graphology—is a poor way to predict personality types, even though it is used by 3,000 United States firms and by a majority of European companies. In a recent study, five graphologists scored no better than chance in predicting the occupations of forty professionals.
Which one of the following is an assumption necessary to the argument?
(A) People in the same occupation usually do not have the same personality type.
(B) Graphology is an effective means of predicting personality types in non-business contexts.
(C) There are more United States firms that do not use graphology than all the United States and European firms that do use it.
(D) There are several other techniques for predicting personality types that are more accurate than graphology.
(E) There is a correspondence between type of personality and choice of occupation.
（2）看到假设的题该如何想呢？？假设到底和前提与结论是个什么关系呢？
A:  1. 假设题的类型不同, 但相同的是line of reasining有gap. 在读CR原文时,要做的一件事是找出文中所设计的事物, 包括名词, 概念, 数字(或比较), 时间等. 这些事物对排除答案也有很大帮助(我在我CR的总结中会提到).
你还要把握原文的推理过程(或叫逻辑关系). 第一句话:结论, 涉及概念: G, personality, companies. 第二句话:依据, 涉及概念: recent study, occupation. 你应该看到原文的逻辑关系: handwriting did poorly on predicting occupation-->handwriting is a poor way to predict personality. 两个概念不同, 中间有个gap, 既occupation<==>personality.
我再举个例子说明这类题型:都说一班的学生比二班的聪明,可是张学友怎么就比一班的王胖子聪明呢?assumption就是张学友是二班的.这个gap不填上就没有结论了.

myice

5. No senator spoke at the convention unless he or she was a Democrat. No Democrat both spoke at the convention and was a senator
Which one of the following conclusions can be correctly drawn from the statements above?
(A) N one but senators spoke at the convention.
(B) No Democrat spoke at the convention.
(C) Only Democrats spoke at the convention.
(D) No senator spoke at the convention.
(E) Some Democrat senators spoke at the convention.
. 还是充分必要条件.
If A, then B, 则A(充分)-->B(必要)
A only if B, 则A(充分)-->B(必要)
not A unless B, 则A(充分)-->B(必要)
原文的逻辑关系为Senator spoke --> democrat; democrat-->not spoke at the convention and a senator at the same time
命题的逆否命题相同: not democrat-->not speak as a senator; both spoke and a senator-->not a democrat.
两个结合起来, 就是:不是民主党的参议员不在convention发言, 民主党不会又发言又是参议员. 则答案为D

:  anyway, 所谓充分必要,顾名思义,充分就是某个条件,如果其成立,足以推出某个结论.举例:
天黑了{A},(所以)我们不能打球了{B}. "天黑了"就是充分条件. 其逻辑关系为有A一定有B. 注意到充分条件可以不只一个,比如说"下雨了"也是一个充分条件.
必要条件既如果没有此条件,推不出结论,或某个结论成立,此条件必然成立. 举例:吃饭{A}才能饱{B}. A为必要条件,既不吃饭{非A},就一定不饱{非B}. 其逻辑关系为有B一定有A. 注意A不是充分条件,因为A本身不足以推出B,还要吃地够多才行.
还有一种是充分必要条件: A<-->B

myice

6. The program to control the entry of illegal drugs into the country was a failure in 1987. If the program had been successful, the wholesale price of most illegal drugs would not have dropped substantially in 1987.
13. The argument in the passage depends on which of the following assumptions?
(A) The supply of illegal drugs dropped substantially in 1987.
(B) The price paid for most illegal drugs by the average consumer did not drop substantially in 1987.
(C) Domestic production of illegal drugs increased at a higher rate than did the entry of such drugs into the country.
(D) The wholesale price of a few illegal drugs increased substantially in 1987.
(E) A drop in demand for most illegal drugs in 1987 was not the sole cause of the drop in their wholesale price.
ans: E
assumption就是隐含的必要条件. 如果对其取非,否定此条件,那么就不能推出原文的conclusion. 即A-->B ==> 非B--非A, B在此为assumption.
很多假设题目的答案是很多假设其中的一个,别比如说:考砸了-->没复习好. assumption就有很多: 不是考前没睡好造成的;不是考试时晕到了;不是考试时睡着了; 复习好就能考好等等. 答案就是其中一个,比相当于一个集合中的factor.
GMAT所要求的common sense只有很窄的范围, 比如说inflation-->总体物价上涨, low wage and severe working condition-->unsatisfied employees. 这类常理是肯定正确的, 而且不需要任何专业常识

A:  排除他因
A: 供求决定价格，如果需求的减少不是导致降价的唯一原因，则一定是供给太多了，那就可以理解了
Q: If the program had been successful, the wholesale price of most illegal drugs would not have dropped substantially in 1987
==>The program to control the entry of illegal drugs into the country was a failure in 1987.
对吗？
如果是这样的话，assumption 应该是对结论的，而不是对论据的，对吗？而答案却是对论据的，是不是有问题？
A: assumption对结论是什么意思? assumption本身是结论的必要条件.  
你找到的原文的逻辑关系是正确的. 正如renprince和cranberry所说, 此题是典型的排除它因类型. 如果有其它原因对结论有绝对的影响, 那么原文对program的结论不成立. 简单的例子: .我节食失败了. 因为如果我节食成功, 我就不会更胖了. 这里就忽略了一个问题, 其错误在于: 节食很可能只是减肥的一个必要条件, 而原文把它作为充分条件. 即节食-->减肥==>非减肥-->节食失败. 所以要使原文结论成立, 必须假设节食为充分条件,既没有其它因素对减肥起作用. 如果问weaken, 那可以是体内激素失调造成了更胖, 既节食和极素平衡同为必要条件.
你要记住此类题型, 有了感觉以后根本无须考虑很多, ETS送分给你.

myice

7. . When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast. of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use. the vast majority of those who test positive will be people who have used cocaine.
A reasoning error in the argument is that the argument
(A) attempts to infer a value judgment from purely factual premises.
(B) attributes to every member of the population the properties of the average member of the population.
(C) fails to take into account what proportion of the population have used cocaine.
(D) ignores the fact that some cocaine users do not test positive.
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine.
答案：C，我一见数学题，人就晕，就搞不明白这些数字 是怎么来的怎么去的。
谢谢。
A:
A:
A: 原文说5%的不用coke的人会被误测, 而99%的用coke的人会被测出来.所以在一个sample人群中测coke, 被测出positive的人中大多数是用coke的人. 这里可以看出来positive的人包括5%不用coke而被误测的人加上99%用coke的人. 结论是99%用coke的人要多于5%不用coke的人.  这里的错误是我们只知道两个百分比, 没有绝对的数值, 而且两个百分比的基数不同, 无法比较. 如果不用coke的人有一万个, 用的有一百个, 那么positive的人有10000*5%+100*99%=599.般其中误测的就多于正确的.