这题我在那回复了。反正我现在做逻辑题的思路都是先理清题意抽象成逻辑或者数学模型，就跟解应用题一样，这样就避免自己被那些很复杂的语言绕住，因为数学公式对我来说很straightforward. 所以那道题我的解释就是纯数学， control的概念： 目标：研究变量(variant) x和变量y的关系 (x is called an independent variant; y is called a dependent variant. ) 我们知道y=f(x, a, b, c, ....) y is a function of x, a, b, c, ... 那么就需要令a, b, c, ...统统恒定，变成常量(constant)，这样就是： y=f(x) 以上是这道题的逻辑基础，或者数学基础，想明白了就特简单。
http://forum.chasedream.com/GMAT_CR/thread-57558-1-1.html 非常trciky的题目，做了这道题目我越发的感觉，逻辑很重要的一方面是对内容的准确理解，越难的题目越是如此。很多NN都栽在这道题目上了，特此还有2位大N为此辩论写了AA呢！你有火眼金睛看出大N哪里出错了？ -- by 会员 yiayia (2012/3/8 21:38:31)
-- by 会员 babybearmm (2012/3/9 2:58:58)
Smithtown University’s fund-raisers succeeded in getting donations from 80 percent of the potential donors they contacted. This success rate, exceptionally high for university fund-raisers, does not indicate that they were doing a good job. On the contrary, since the people most likely to donate are those who have donated in the past, good fundraisers constantly try less-likely prospects in an effort to expand the donor base. The high success rate shows insufficient canvassing effort.
Which of the following, if true, provides more support for the argument?
A. Smithtown University’s fund-raisers were successful in their contacts with potential donors who had never given before about as frequently as were fundraisers for other universities in their contacts with such people.
B. This year the average size of the donations to Smithtown University from new donors when the university’s fund-raisers had contacted was larger than the average size of donations from donors who had given to the university before.
C. This year most of the donations that came to Smithtown University from people who had previously donated to it were made without the university’s fund-raisers having made any contact with the donors.
D. The majority of the donations that fund-raisers succeeded in getting for Smithtown University this year were from donors who had never given to the university before
E. More than half of the money raised by Smithtown University’s fund-raisers came from donors who had never previously donated to the university.
Conclusion. SU not good fundraiser
Premise 1. (fact) SU high successful rate
Premise 2. good fundraiser try less-likely-donors
由Premise 2. 作者潜在的含义是：
for good fundraiser: try many less-likely-donors <------> low successful rate
可以看出，作者推出conclusion基于的直接assumption是：
ASSUMPTION: high successful rate <-------> not try many less-likely-donors (in this sense, not good fundraiser)
这就是assumption，说白了，就是把"successful rate"和"try less-likely-donors"架桥。
于是我们进行prephrase，推测正确选项应该是validate this assumption.
那么A，就是明显满足。A干的事情，在科学研究上叫做control，将其他条件的影响限定为0。A说的是，在less-likely-donors这部分pool里，SU和别的学校的successful rate相等。
如果同学认为以上control的概念不是那么straightforward，我再用数学公式来解释
咱要讨论的"successful rate"是overall successful rate，设为r
分为两个sample pools:
Pool 1. less-likely-donor 设success rate为 r1 这部分人占的比例x%
Pool 2. more-likely-donor 设success rate为 r2 这部分人占的比例(100-x)%
条件r1<r2
r=r1*x% + r2*(100-x)%
作者的逻辑是：r大，就证明x小（r2那一项的“比重”大），也就是说not good fundraiser
但是式的变量太多，决定r的变量，除了x之外，还有r1, r2.
当r1, r2恒定的时候，基于r1<r2，我们从逻辑上可以完美推出r和x之间的关系，如作者所述(r大，则x小)。
所以，A选项干的事情，就是令r1恒定("were successful ... as frequently as")。
C is totally out-of-scope.
以上讨论的范围是那些have been contacted的人（分为less-likely-donor和more-likely-donor两部分），C说的是关于people not having been contacted. 所以out-of-scope.
把baby姐姐的粘贴过来了，恩恩，懂了，这样架桥或者是按数学来推是一目了然~！！ | 
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发表于 2012-3-9 03:22:09
楼主
发表于 2012-3-9 08:11:34
保持住哦！一起加油！！
要努力了！！！