2018年GMAT年度回顾——逻辑|沃邦年终总结


来源:   时间:2019-02-01 13:13:31

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数据来源OG2018
 
在GMAT经历了2018年的改革以后,verbal部分的题数从原来的41题减少到了36题,阅读部分依然是4篇(13-14题),逻辑题数基本和改革前变化不大(9-10题),而语法题则相对减少较多(12-13题),当然每个考生考试时遇到情况不同,会有1-2题的波动,但是总体阅读部分比重增加,而逻辑在三块中占比最少。当然这并不意味着大家可以对逻辑掉以轻心,因为在阅读和IR中也会出现一部分逻辑题型,写作则很大程度上和逻辑的思路重合。所以从整体来看,逻辑还是贯穿于整个考试中,如果说语法是基础,那么逻辑就是训练同学们critical thinking的能力,对整个Verbal部分有着举足轻重的影响。
 
从题型分布来看,逻辑中最常考的还是evaluation argument中的加强和削弱题,而相对argument construction中的句子作用题和归纳题考察较少,其余题型比重差别不大。但是无论题型如何变化,在做题时需要抓住一个关键,就是找到题目的逻辑链,即通过何种前提推导出什么结论。所有的题型都是基于这个逻辑链,比如我们需要去加强或是削弱某一个plan,或是为argument找出必要条件。当刷题到一定的程度,我们可以对答案有一定的预判,往往某种题型的正确答案都会有一些逻辑上的共性,接下去我们就从3个不同题型来分别做具体讲解。
 
例1.  Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils that are much older than the earliest birdlike dinosaur fossils that have been found.
Which of the following is an assumption on which the argument relies?
(A) The birdlike dinosaurs have no living descendants.
(B) There are no flightless dinosaur species that have the distinctive structural features shared by birds and birdlike dinosaurs.
(C) There are no birdlike dinosaur fossils that are older than the bird fossils but have not yet been unearthed.
(D) It could not have been the case that some birds were descended from one of the birdlike dinosaur species and other birds from another.
(E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features. 

解析:先找出题目中的逻辑链,即通过化石发现存在鸟的化石要早于最早的类鸟恐龙的化石,所以结论是鸟是此种类鸟恐龙后代的说法不成立。问题是要为这个argument找出一个assumption,即必要条件。这道题的关键信息在于通过比较化石时间来确定鸟是否为恐龙的后代,那么答案的方向一定和时间有关。A选项在讨论类鸟恐龙是否有活着的后代,和逻辑链无关。B选项重点在讨论是否有恐龙存在和鸟和类鸟恐龙一样的structural features,也和讨论重心无关。D选项在说鸟类不可能是不同类鸟恐龙种类的后代,但是题目中所讨论的重点是鸟类是否是恐龙的后代,并不在于恐龙种类是否不同,所以也无关。E选项是说鸟类不可能是那些和他们的structural features不同的恐龙的后代,但是与逻辑链中的关于化石时间的问题没有关系,也排除。C选项是说不存在未出土的早于鸟类化石的类鸟恐龙化石。C选项首先和逻辑链中关于讨论化石时间吻合,并且符合assumption题型中的“排除他因”。我们对C选项取非,就是说其实存在早于鸟类化石的类鸟恐龙化石,只不过没有出土而已,那么结论就无法成立。C选项排除了一种使结论无法成立的可能性,即为argument成立的必要条件。
 
例2. Tiger sharks are common in the waters surrounding Tenare Island.  Usually tiger sharks feed on smaller sharks, but sometimes they have attacked tourists swimming and surfing at Tenare's beaches. This has hurt Tenare's tourism industry, which is second only to its fishing industry in annual revenues.  In order to help the economy, therefore, the mayor of the island has proposed an ongoing program to kill any tiger sharks within a mile of the beaches.
Which of the following, if true, most strongly calls into question the likelihood that implementation of the mayor's proposal will have the desired consequence?
(A) Even if not all the tiger sharks that come close to the beaches are killed, the existence of the program would reassure tourists.
(B) Business owners who depend on tourism are willing to pay most of the cost of implementing the program.
(C) Tourists come to Tenare Island for its beaches, even though the island features a number of other tourist attractions.
(D) The small sharks on which tiger sharks prey feed on fish that are commercially important to the island's fisheries.
(E) Not all tourists who come to Tenare Island enjoy swimming or surfing.

解析:题目中的逻辑链为tiger sharks因为攻击游客而影响旅游业,所以市长决定把靠近沙滩的tiger sharks都杀死,这样做就能提高当地经济。题目需要我们找出一个选项来削弱市长提出的建议,也就是如果选项成立,那么该建议能够成功的可能性降低,即econoomy无法提高。我们抓住这个重心去看选项,A说的是即使不能杀死所有靠近沙滩的tiger sharks,市长的这个举动也可以对游客有所安慰。A是在加强结论成立的可能性而非削弱,直接排除。B重点是说业主愿意承担市长的这项program的费用,但是并没有讨论program是否可以成功,无关排除。C在解释游客为什么来这个沙滩,并没有涉及市长的建议,排除。D说tiger sharks吃的那些small sharks会吃一些小鱼,而这些鱼对当地渔业在经济上很重要。D选项乍看貌似无关,但是仔细看渔业在原文中有提到,它是当地最大的年收入来源。也就是说虽然tiger sharks减少了,但是直接使得鱼的数量减少(以它为食的small sharks变多),那么渔业就会受影响。所以economy就不一定会提高了,正确。E选项讨论重点和economy无关,直接排除。
 
例3. Capuchin monkeys often rub their bodies with a certain type of millipede. Laboratory tests show that secretions from the bodies of these millipedes are rich in two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate capuchins. Some scientists hypothesize that the monkeys rub their bodies with the millipedes because doing so helps protect them from mosquitoes.
Which of the following, if true, most strongly supports the argument?
(A) A single millipede often gets passed around among several capuchins, all of whom rub their bodies with it.
(B) The two chemicals that repel mosquitoes also repel several other varieties of insects.
(C) The capuchins rarely rub their bodies with the millipedes except during the rainy season, when mosquito populations are at their peak.
(D) Although the capuchins eat several species of insects, they do not eat the type of millipede they use to rub their bodies.
(E) The two insect-repelling chemicals in the secretions of the millipedes are carcinogenic for humans but do not appear to be carcinogenic for capuchins.

解析:文中逻辑链是某种猴子会用m来擦身体,m中会分泌某种物质有驱蚊作用,而蚊子身上的寄生虫会使猴子虚弱,所以结论是猴子用m来擦身体主要是为了防蚊。题目要求我们找出可以支持argument的选项,即选项成立可以提高argument成立的可能性,我们选出的答案一定是加强对于用m擦身体和防蚊之间的联系。A选项重点在于一个m可以在不同的猴子中传递,但是并未提到防蚊,排除。B选项讨论了other varieties of insects, 偏离讨论重点,排除。C选项说猴子除了雨季很少擦身体,而雨季是蚊子最多的时候,加强了猴子的举动和蚊子之间的联系,保留。D在说猴子不吃m这种虫子,并未增强逻辑链的关系,排除。E说m身上分泌的化学物质对于人类有致癌作用,和逻辑链无关,排除。
 

 总结 

 
通过上述三个题型分析,大家会发现无论是加强,削弱或者假设题,解题的关键还是在于把握文中的逻辑链,答案的重点往往和逻辑链中的关键信息有关,而只要涉及到和逻辑链无关的选项可以轻松排除。假设题和加强题在思路上有一定的共性,我们可以认为假设题是百分之百的加强(非他不可),而加强题只要做到部分加强即可(锦上添花),而削弱题和前两种题型的思路正好相反。所以逻辑题并没有大家想象中的那么可怕,虽然有些题目给的信息很复杂,我们要做的就是在大脑中迅速简化这些复杂的信息,用自己的话概括出一个简单的逻辑关系,把握住这个关键点,一旦这种关系明确了,我们就不会被一些无关信息所干扰了。我们的题目千变万化,但是思路却是共通的。建议大家不要只是盲目刷题,要更多的去总结规律,这样才能做到事半功倍。最后祝考G的同学们都可以杀G成功,进入自己理想的学府! 

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延伸阅读

2018年GMAT年度回顾——阅读|沃邦年终总结

2018年GMAT年度回顾——语法|沃邦年终总结

2018年GMAT年度回顾——数学|沃邦年终总结

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