两道逻辑题看破assumption题型

在备考GMAT逻辑的过程中，大家是否经历过：

1.完全看不懂题目说啥呀？也不知道要我干嘛？？

2.读懂了但是就是选不对答案？

3.读懂了，也做对了，但是不知道为啥做对的？

讲真，都是这么过来的。大家应该也是经历了人生三境界——先是“昨夜西风凋碧树，独上高楼，望尽天涯路”，然后“衣带渐宽终不悔，为伊消得人憔悴”，最后“众里寻他千百度，蓦然回首，那人却在灯火阑珊处”。我一直讲，大多数人应该都到了第二重境界，而止步于此。

刷题多了，大多数人都觉得CR部分strengthen（support）、weaken、evaluation或explanation都不是最难的，反倒是assumption题型，刷题再多也没找着“套路”。作为经验之谈，或者在考场应付考试而言，平时课堂上传授的方法还是比较实用的——“取非验证法”（negation）。当然，单纯为提高做题速度的话，采用“五排三原则”先排掉三个选项是非常容易的，还剩下两个选项再采用“取非”的方法排掉另外一个，噢，剩下的就是我们需要的。

但是，如果真想搞懂这类题，还得有严密的推理。而不是仅仅停留在只是做对了题目，但是为什么对也说不上来。今天探讨一种解assumption题型的推理方法——找logic gap。直接上题：

例1：

A recent report determined that although only three percent of drivers on Maryland

highways equipped their vehicles with radar detectors, thirty-three percent of all

vehicles ticketed for exceeding the speed limit were equipped with them. Clearly,

drivers who equip their vehicles with radar detectors are more likely to exceed the

speed limit regularly than are drivers who do not.

The conclusion drawn above depends on which of the following assumptions?

(A) Drivers who equip their vehicles with radar detectors are less likely to be ticketed

for exceeding the speed limit than are drivers who do not.

(B) Drivers who are ticketed for exceeding the speed limit are more likely to exceed

the speed limit regularly than are drivers who are not ticketed.

(C) The number of vehicles that were ticketed for exceeding the speed limit was

greater than the number of vehicles that were equipped with radar detectors.

(D) Many of the vehicles that were ticketed for exceeding the speed limit were

ticketed more than once in the time period covered by the report.

(E) Drivers on Maryland highways exceeded the speed limit more often than did

drivers on other state highways not covered in the report.

分析：“所有的车里有3%装雷达，超速被罚（ticketed for exceeding the speed limit ）的车里有33%装了雷达，换句话说前提是装雷达的司机更容易超速被罚，但结论说装雷达的司机更容易超速。”这里的logic gap：一个是超速被罚，一个是超速 ，这是两个概念。因此，简单搭桥就填补了这个gap，即“装雷达的司机更容易被罚+被罚的司机更可能超速=装雷达的司机更容易超速”，所以选B。

例2：

Researchers have found that when very overweight people, who tend to have relatively low metabolic rates, lose weight primarily through dieting, their metabolisms generally remain unchanged. They will thus burn significantly fewer calories at the new weight than do people whose weight is normally at that level. Such newly thin persons will, therefore, ultimately regain weight until their body size again matches their metabolic rate.

The conclusion of the argument above depends on which of the following assumptions?

(A) Relatively few very overweight people who have dieted down to a new weight

tend to continue to consume substantially fewer calories than do people whose normal

weight is at that level.

(B) The metabolisms of people who are usually not overweight are much more able to

vary than the metabolisms of people who have been very overweight.

(C) The amount of calories that a person usually burns in a day is determined more by

the amount that is consumed that day than by the current weight of the individual.

(D) Researchers have not yet determined whether the metabolic rates of formerly very

overweight individuals can be accelerated by means of chemical agents.

(E) Because of the constancy of their metabolic rates, people who are at their usual

weight normally have as much difficulty gaining weight as they do losing it.

分析：“研究者发现胖人往往新陈代谢慢，靠节食减肥，他们的新陈代谢一般不变。因此他们减肥后仍比正常人燃烧更少卡路里。因此这些人最终还会增肥直到体重和新陈代谢率相当。”前提是减下来后比正常人燃烧更少卡路里，结论就跳跃到最终会胖回去。很明显logic gap是还需要再多吃（虽然燃烧少了，但是如果不吃，至少能维持在减下来的体重呀）。填补上这个必要条件才能说明会胖回去。即“减肥后燃烧更少卡路里+大多数减肥后吃更多含卡路里的食物= 最终会打回原形”。（burn less + consume more = regain）因此就选A了。

通过这两道题，相信我们对假设题型有点感觉了。万变不离其宗，大家只需明白一个道理：assumption题就是要补充一个necessary condition，因此不管是用“取非验证”还是“找logic gap”都能搞定。

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