请原谅我哪些钻牛角尖的题目。。T,T 感激。。

199249712

第二个也懂了。。。我粗心了。比较错误。。。

199249712

Questions49-50
Joseph: My encyclopedia saysthat the mathematician Pierre de Fermat died in 1665 without leaving behind anywritten proof for a theorem that he claimed nonetheless to have proved. Probably this alleged theorem simplycannot be proved, since---as the article points out---no one else has beenable to prove it. Therefore it is likely that Fermat was either lying or elsemistaken when he made his claim.
Laura: Your encyclopedia is outof date. Recently someone has in fact proved Fermat’s theorem. And since thetheorem is provable, your claim---that Fermat was lying or mistaken---clearlyis wrong.
50. Which one of the followingmost accurately describes a reasoning error in Laura’s argument?
(A) It purports to establishits conclusion by making a claim that, if true, would actually contradict thatconclusion.
(B) Itmistakenly assumes that the quality of a person’s character can legitimately betaken to guarantee the accuracy of the claims that person has made.
(C) It mistakes something that is necessary for itsconclusion to follow for something that ensures that the conclusion follows.
(D) It uses the term “provable”without defining it.
(E) It fails to distinguishbetween a true claim that has mistakenly between believed to be false and afalse claim that has mistakenly been believed to be true.








………………错误率好稳定啊 5/5/4

这道。。开始是属于完全没有思路的内种。。。 选项都太抽象啦

姐姐看这个结果正确吗。。。求确认。。求姐姐的思路。。。
A+B=C

something that ensures that the conclusion follows.

B×
所以A+B=!C
B就成了
something that is necessary for its conclusion
so
It mistakes something that is necessary for itsconclusion to follow for something that ensures that the conclusion follows.

babybearmm

这题就是充分条件和必要条件。

Joseph：

Fermat died without any written proof
                                                                     } Fermat's theorem is NOT provable -----> Fermat was lying or making mistake (he alleged to have proved it)
no one has been able to prove

Laura:
someone recently proved ----> Fermat's theorem is provable ----> Fermat was NOT lying or .... (by claiming he had proved it)

You know, Laura's argument is unsound. By noting that someone is able to prove, we CANNOT conclude that Fermat himself was able to prove. Perhaps he was unable to prove, and he told a lie in claiming that he had proved it.

On the other hand, Joseph's argument is sound (I mean the last arrow, from Fermat's theorem is NOT provable to Fermat was lying or making mistake (he alleged to have proved it)), because if Fermat was honest, his theorem must be provable. Therefore, by noting that his theorem is not provable, Joseph concludes that Fermat was dishonest.

A = "Fermat's theorem is NOT provable"
B = "Fermat was lying or ..."

Joseph:      A----->B                      A是B的充分(sufficient)条件，B是A的必要(necessary)条件
Laura:        No A -----> No B

以上，抽象一下吧。就说一个命题"A--->B"（由A推出B），这里面：A是B的充分(sufficient)条件，B是A的必要(necessary)条件
逆命题是"B--->A"，否命题是"no A ----> no B"，逆否命题是"no B ---> no A"
一个命题和他的逆否命题，是等效的。
"A--->B" 等效于 "no B ---> no A"

那么上面，Joseph的"A--->B"能站住脚，而Laura提出的是这个命题的否命题"no A ----> no B"，未必站得住脚。当且仅当A和B互为充要条件的时候，才能站住脚。

(btw:sorry后面这片我不知道怎么用英文说，我是小时候学奥数学的逻辑，用的中文。我是喜欢把那些长串英文用数学符号表示，就像解数学应用题设x, y variables一样，然后模式化推理，就像列方程解方程一样。这样比较准确快捷，因为不用通过英文长串语言去思考，就节省了大脑很多内存。）

Questions49-50
Joseph: My encyclopedia saysthat the mathematician Pierre de Fermat died in 1665 without leaving behind anywritten proof for a theorem that he claimed nonetheless to have proved. Probably this alleged theorem simplycannot be proved, since---as the article points out---no one else has beenable to prove it. Therefore it is likely that Fermat was either lying or elsemistaken when he made his claim.
Laura: Your encyclopedia is outof date. Recently someone has in fact proved Fermat’s theorem. And since thetheorem is provable, your claim---that Fermat was lying or mistaken---clearlyis wrong.
50. Which one of the followingmost accurately describes a reasoning error in Laura’s argument?
(A) It purports to establishits conclusion by making a claim that, if true, would actually contradict thatconclusion.
(B) Itmistakenly assumes that the quality of a person’s character can legitimately betaken to guarantee the accuracy of the claims that person has made.
(C) It mistakes something that is necessary for itsconclusion to follow for something that ensures that the conclusion follows.
(D) It uses the term “provable”without defining it.
(E) It fails to distinguishbetween a true claim that has mistakenly between believed to be false and afalse claim that has mistakenly been believed to be true.








………………错误率好稳定啊 5/5/4

这道。。开始是属于完全没有思路的内种。。。 选项都太抽象啦

姐姐看这个结果正确吗。。。求确认。。求姐姐的思路。。。
A+B=C

something that ensures that the conclusion follows.

B×
所以A+B=!C
B就成了
something that is necessary for its conclusion
so
It mistakes something that is necessary for itsconclusion to follow for something that ensures that the conclusion follows.

-- by 会员 199249712 (2012/3/28 19:01:50)

199249712

Probably this alleged theorem simplycannot be proved,

Therefore it is likely that Fermat was either lying or elsemistaken when he made his claim.

偶明白了…… 偶把结论弄错了…………谢谢姐姐~！

babybearmm

You got it!

Probably this alleged theorem simplycannot be proved,

Therefore it is likely that Fermat was either lying or elsemistaken when he made his claim.

偶明白了…… 偶把结论弄错了…………谢谢姐姐~！

-- by 会员 199249712 (2012/3/29 8:14:45)

199249712

66.
A recent survey showed that many workers in acertain company are dissatisfiedwith their jobs. The survey also showed thatmost of the dissatisfied workersbelieve that they have little control overtheir job assignments. Therefore, toincrease workers’ job satisfaction thecompany’s management need onlyconcentrated on changing workers’ beliefsregarding the degree of control theyhave over their job assignment.
Which one of thefollowing, if also shown by the survey, would most seriouslycall into questionthe conclusion made by the author of the passage?
(A) The dissatisfied workers feel that theirwagesare too low and working conditions are unsatisfactory.

(D)Most people in company management believe that theworkers already have toomuch control over their work.

66. To be honest，我的直觉是A，然后还是花了4min来确认（主要是确定排除D）....
如果要说快捷的解题方法，我觉得就是抓住结论（相信直觉还是没错的）:
Therefore, to increase workers job satisfactionthe company’s management need onlyconcentrate on changing workers’ beliefs regarding the degree of control theyhave over their job assignments.
In order to weaken the conclusion, we should show that there are other factors(independent of feeling self-controlled) that contribute to workers'satisfaction. Hence Choice A is the answer.

如果你要问我D为啥错，我还是借助心爱的数学玩具来解释吧：
Let Y be "worker's satisfaction" and X be "feeling self-controlled".Each of X and Y has a value of 0 or 1, with 0 being "no" and 1 being"yes". Set up a 2X2 matrix of joint probability pxy:

Y=1	p01	p11
Y=0	p00	p10
joint probability	X=0	X=1

Now, translate all the english language to mathematical expressions:
many workers ... are dissatisfied with theirjobs
p00+p10 islarge          (1)
The survey also showed that most of thedissatisfied workers believe that they have little control over their jobassignments.
p00/p10> 1               (2)
D is saying:
(D)Most people in company management believe thatthe workers already have too much control over their work.
(p10+p11)/(p00+p01)>1           (D)
note: 不好意思，我发现我在写这篇分析的时候，把D选项意思理解错了。我当时理解成了说most workers feel they already have self-control.还是有点区别的，这里说的不是对自己的感受评价，而是说对公司workers整体的感受评价。那么D选项就更加无关了。

As we know from statistics, "variables X and Y are positivelycorrelated" is equivalent to "the odds ratio is significantly largerthan 1". That is:
odds ratio = (p00*p11)/(p01*p10)> 1            (*)
However, from what we know, i.e.(1) and (2),  we CANNOT conclude (*). Inother words, data could simply be  coincidence, NOT a manifestation ofcausal relationship ("not feeling self-controlled" leads to "nosatisfaction")
Also, (D) has NOTHING to do with (*). In other words, D neither strengthens norweakens the argument.

Also, there could be many other factors serving as determinants ofsatisfaction. In mathematical expression, Y is a function （函数）of its determinants.
Y=f(X, A, B, C, ...)
or even without X:
Y=f(A, B, C, ...)

In summary, my points are:
(a) It is dubitable whether X is a determinant of Y;
(b) There are other determinants of Y, so X is NOT the ONLY determinant.
Therefore, Choice D is incorrect, and Choice A is correct by pointing out otherdeterminants.

btw: 我觉得这种joint probability matrix -- odds ratio 的统计学思路解CR题挺有用的，因为CR很多题就是研究variables之间是否存在相互联系。而likelyhood的数学表示就是odds ratio，这也会极大地简化咱的思维过程，让内在的逻辑暴露得更明显。一个类似的题目：
http://forum.chasedream.com/GMAT_CR/thread-695574-1-1.html

199249712

再次狠狠的研究了一下姐姐的思路…… 懂了后觉得太赞了啊 尤其是kaplan的题……
~！！ 姐姐跟Yiayia哥绝对是大神啊。。

Choi: All other factors being equal, childrenwhose parents earned doctorates are more likely to earn a doctorate thanchildren whose parents who did not earn doctorates.

Harts: But consider this: Over 70 percent ofall doctorate holders do not have a parent who also holds a doctorate.

Which of the following is the most accurate evaluationof Hart's reply?

a. It establishes that Choi's claim is anexaggeration.
b. If true, it effecively demonstrates thatChoi's claim cannot be accurate.
c. It is consisitent with Choi's claim.
d. It provides alternative reasons foraccepting Choi's claim.
e. It mistakes what is necessary for an eventwith what is sufficient to determine that the event will occur.                                  

[attachimg]98343[/attachimg]

[attachimg]98344[/attachimg]

对应狒狒66题

199249712

60. One of themore reliable methods of determining regional climatic conditionsinprehistoric periods is to examine plant pollen trapped in glacial iceduringancient times. By comparing such pollen samples with spores take frommodernvegetation, scientists can figure out approximately what the weather waslike atthe time of pollen deposition. Furthermore, by submitting theprehistoricsamples to radiocarbon dating techniques, we can also determine whencertainclimatic conditions were prevalent in that portion of the globe.
Which one of thefollowing may be inferred from the information in the passage?
(A) The earth hasundergone several glacial periods.
(B)Radiocarbon dating can be corroborated by glacialevidence.
(C) Similaritiesbetween prehistoric and contemporary climates do not exist.
(D) Pollen depositionis a fairly continuous process.
(E) Certain flora are reliably associatedwithparticular climatic conditions.

60.这题关键是读懂，就像scientific RC.
According to the stimulus, glacial evidence (i.e. the pollen samples) can tell what type of climate was at that time, and carbondating can tell "when certain climaticconditions were prevalent in that portion of the globe"
For example, with pollen samples, we can tell that at x million years ago(associated with the pollen sample), the climate is "hot and humid".And with carbon dating, we can tell that this particular type of climate("hot and humid") was prevalent in that place from x1 million yearsago to x2 million years ago.
Therefore, these two methods give different information. Hence Choice B iswrong.

Choice E is correct. Because scientists can tell the climate type from thepollen samples, we can safely infer that there are certain flowers associatedwith a particular climate type.

199249712

59. Top college graduates are having moredifficulty demonstratingtheir superiority to prospectiveemployersthan did the top students of twenty years ago when an honors degreewasdistinction enough. Today’s employers are less impressed with the honorsdegree.Twenty years ago no more than 10 percent of a given class graduatedwith honors.Today, however, because of grade inflation, the honors degree goesto more than50 percent of a graduating class. Therefore, to restore confidencein thedegrees they award, colleges must take steps to control grade inflation.
Which one of the following is an assumption that, if true, would supporttheconclusion in the passage?
(A) Today’s studentsare not higher achieversthan the students of twenty years ago.
(B) Awarding too many honors degrees causescolleges toinflate grades.
(C) Today’s employers rely on honors ranking in making their hiringdecisions.
(D) It is not easy for students with low grades to obtain jobs.
(E) Colleges must make employers aware of the criteria used todetermine whoreceives an honor degree.

59这题我刚也做错了，错选了E。看答案发现，A是典型的defender assumption。
B错是因为，题目说了"inflategrades ----> too many honors degree"，因果关系是这样的，B把因果关系颠倒了，这属于out-of-scope，不能作为assumption. 另外"inflate grades ----> toomany honors degree"并不是论证的核心，而是cause of the cause.

“那道SC，A的that 能不能指代goal呢 like的用法到底对不对呢”
mm啊，一个压根就不对的句子，你问我这里面"that"指代什么，我咋说？永远别去justify错误句子的结构。
我就是从意思上判断，
the youth has this particular goal
is compared to
the earlier generations had this particular goal
所以必须用as啊，"like that"无论如何都不对，甭管that指什么。

199249712

70. A low-pressure weather system is approaching Plainville; rainfall results from about 70 percent of such systems in the Plainville
area. Moreover, the current season, spring, is the time of year in which thundershowers, which sometimes result from low-pressure systems, are most likely to occur in Plainville.

Knowing which one of the following, in addition to the information above, would be most useful for determine the probability that Plainville will have a thundershower soon?


A.the percentage of thundershowers in Plainville that occur in the spring
B.the percentage of spring rainfalls in Plainville that are thundershowers ?
C.the percentage of thundershowers in Plainville that result from low-pressure systems
D.whether low-pressure systems in other areas are associated with rainfall
E.whether Plainville has more or fewer thundershowers each spring than do near by towns


额。。我的狒狒上写的这道题的答案是B
但是在解析上的答案是C


后来想了一下 觉得C是对的。。


我的思路是：
l/r=70
t/l=C
so t/r=70C

其中   l=low pressure
        t=thundershowers
        r=rainfall

我想错的主要原因是由于我们读错了第二句话的含义：
rainfall results from about 70 percent of such systems inthe Plainvillearea.
70%修饰的是low pressure
不是rainfall
所以比例是反的 所以可以相乘 相乘后就可以把分母消掉了

酱紫。。。