几道有疑问的逻辑题

alzn2765

选自新东方的《GMAT逻辑推理分类思维训练及试题解析》174页38题

The theory that the impact of a giant meteorite caused the extinction of the dinosaurs is based on evidence that a could of dust from the impact blocked off sunlight around the globe for months, reducing temperatures and destroying the dinosaurs' food supply.
Which of the following, if ture, casts the most serious doubt on the theory above?

A.Dinosaurs are believed to have been cold-blooded and thus very sensitive to any temperature change.
B. Some dinosaurs lived in regions where their food supply was not well adapted for long periods of cold and darkness.
C. Many large animals that exited during the time of the dinosaurs and shared a common food supply with them continued to populate the Earth long after the extinction of the dinosaurs.
D. A large volcanic explosion that strewed dust in the air and blocked out sunlight was the cause of death of animals within hundreds of miles of the eruption.
E. Many of the largest dinosaurs were herbivorous relying exclusively on vegetation for their dietary needs.








官方答案是C

我的疑问是C选项明显是一个同因异果的削弱。但是从题干中我感觉这道题是一个果因推理啊！明显这道题的结论是“彗星撞地球导致恐龙灭绝”，这是果。前提是“彗星雾霾导致降温和砸了饭碗”，这是因。这不是一个明显的果因推理吗？可C选项是一个明显的同因异果-“同样雾霾有的动物咋没死？”。同因异果不是不能削弱果因推理吗？

虽然D选项并不完美（只解释了有可能导致方圆几百公里的动物死光光，不足以解释全球恐龙一起死），但是D选项至少给了一个“他因”用来削弱结论-不是彗星导致了恐龙灭绝，有可能是火山爆发导致的雾霾。这不是正好削弱了“彗星撞地球导致恐龙灭绝”的结论吗？



选自新东方的《GMAT逻辑推理分类思维训练及试题解析》162页14题
14. On the basis of figures it complies, a citizens’ group argues that congressional members of party X authorize the spending of more taxpayer dollars than do congressional members of Party Y. The group’s figures are based on an analysis of the number of spending bills for which members of Congress vote.
The figures of the citizens’ group will be unreliable as a gauge of which party in Congress spends more taxpayer dollars if which of the following is true?

A) the group weighs all votes for spending bills equally, no matter how much taxpayer money is involved in each bill.
B) The group counts votes for all spending bills, including bills concerning the salaries of members of congress.
C) Most spending bills that members of Party X vote for are passed by Congress.
D) Most spending bills that members of Party X vote for are written and sponsored by members of Party X.
E) All spending bills, before being voted on by Congress, must be approved by committees in which members of both parties participate.




官方答案是A

我的疑问是A肯定没错，我也理解A的意思。但是D为什么跟A比就不好了？我不明白。如果大部分Party X自己vote的提案都是Party X自己出钱赞助的，但不是等于削弱了Party X花了较多纳税人的钱(Taxpayer Dollars)的结论吗？没话他们的钱，花的是自己的钱。
GMAT一般都很喜欢中“偷换概念”的做法，这次明显概念的不同，为什么D就不如A呢？



选自新东方的《GMAT逻辑推理分类思维训练及试题解析》166页22题
22. In a recent study on the connection between brain abnormalities and violent behavior, the researcher examined more than three hundred people who had engaged in unusually violent behavior toward friends and family members. In most of the people studied, the researcher found clues of brain abnormalities, including evidence of past brain injury and physical abnormality. The researcher concluded that evidence of brain abnormalities could be used to predict violent behavior.
Which of the following, if true, would most seriously weaken the researcher’s conclusion?
A．The incidence of brain abnormalities in the general population is as high as that in the group examined.
B．The brain abnormalities discovered in those studied are of two distinct kinds.
C．A wide variety of violent actions were exhibited by those studied.
D．Those studied in the experiment acted violently toward strangers as well as toward people they knew.
E．The study drew its subjects from a large geographical area.


官方答案是A

这道题的削弱逻辑我真没看懂。A选项怎么削弱的结论？


选自新东方的《GMAT逻辑推理分类思维训练及试题解析》184页57题

Companies considering new cost-cutting manufacturing processes often compare the projected results of making the investment against the alternative of not making the investment with costs, selling prices, and share of market remaining constant.

　　Which of the following, assuming that each is a realistic possibility, constitutes the most serious disadvantage for companies of using the method above for evaluating the financial benefit of new manufacturing processes?

　　(A) The costs of materials required by the new process might not be known with certainty.

　　(B) In several years interest rates might go down, reducing the interest costs of borrowing money to pay for the investment.

　　(C) Some cost-cutting processes might require such expensive investments that there would be no net gain for many years, until the investment was paid for by savings in the manufacturing process.

　　(D) Competitors that do invest in a new process might reduce their selling prices and thus take market share away from companies that do not.

　　(E) The period of year chosen for averaging out the cost of the investment might be somewhat longer or shorter, thus affecting the result.

官方答案是D
我不明白的是，D选项说的是其他公司采取了new cost-cutting manufacturing processes会影响市场份额，但是题中说的不是自己公司如何考量吗？即使本公司不采用new cost-cutting manufacturing processes也不代表其他公司不会用啊，所以本公司用不用跟其他公司用不用有关系吗？如果采用完全动态考量，任何method几乎都是不可能的。我选的是E，成本均摊年份长短不同，会导致产品的cost不同，可能会对是否采用new cost-cutting manufacturing processes产生影响，比如我把全部成本分摊在new cost-cutting manufacturing processes采用的第一年，那么第一年的cost就会很高，跟不采用new cost-cutting manufacturing processes相比，可能会看起来第一年亏损很多，导致在company management看起来似乎new cost-cutting manufacturing processes无法justify它自己的价值，从而对new cost-cutting manufacturing processes能否采用产生影响。

这道题我是真的想不明白，也许是我什么地方欠考虑，请大家给我指明方向！谢谢！

jingliu097

我来说说我的看法

我是基于Helr大神的逻辑思路来的

1、果因
果：恐龙灭绝
因：彗星撞击，解释：撞击产生灰尘阻挡阳光，降低了温度和损害了食物来源。
CQ1：他因
CQ2：否定因果关系
C是CQ2，correct
D是看似CQ1，但是是基于因中的解释的，所以我觉得削弱程度没有C强。
判断标准还是要灵活运用吧，Helr大神还说一道题中不会同时出现CQ1和CQ2的，所以我认为这一题新东方出的不是很好吧

2、因果型
因：the number of spending bills for which members of Congress vote X比Y多
果：X spend more taxpayer dollars
CQ1：推翻因
CQ2：无因果关系或一因多果
题目问削弱
A是CQ1，D是他因，题目问的是因的fingue可不可靠，而不是其他

3、统计枚举型（选项必定涉及样本）：
前提：大多数曾经对家人朋友有暴力行为的examees大脑反常
结论：检测大脑反常可以用来推测暴力行为的发生
CQ1：样本代表性
CQ2：样本数量
题目问削弱
A 是CQ1，如果这些曾经有暴力倾向的人中大脑反常率和所有人中大脑反常率一样，那么即说明大脑反常和暴力行为没什么关系
BCD无关
E是加强（样本普适）

4、目标方案型
方案：compare results
目标：evaluate the financial benefit
题目中涉及要保持costs, selling prices, share of market一致
D说competitors可能会使上面两个因素改变，外部环境变了，因此方案不能有效实施
E是评价的指标吧，比如有个五年计划什么的
或者说，以上三个因素是无关变量，需要保持一致以避免其影响，而E中的时间是一个自变量

alzn2765

jingliu097 发表于 2015-6-7 13:54
我来说说我的看法

我是基于Helr大神的逻辑思路来的

谢谢你先！攒人品这么久，终于有人搭理我了

第一题，首先我们对题型的分类是一致的，果因。
但我不太认同C可以起到否定因果关系的作用：C给出的是与恐龙同期的其他动物的生存情况，而不是恐龙自己。其他动物能不能生存和恐龙能不能生存，这是两个无关的讨论啊！就好像你不能用你非常喜欢包子来说明我也一定喜欢包子一样，或者你不能用我家隔壁是否被盗来推断我家是不是也被盗了。除非你能证明你就是我，或者我家跟隔壁是同一家。此题显然没有任何信息说明恐龙与同时期动物是一样的。

D选项我也认同不是一个逻辑上完美无缺的选项（毕竟D只说了局部灭绝，没说全部灭绝），但至少D提供了一个合理的它因。我们都知道GMAT加强和削弱追求的并不是“绝对的否定”或者“像真理一样成立”，而是只需要增大或者减小某个结论成立的可能性即可。最经典的就是“渡鸦成群飞”那道题。

欢迎点评。

alzn2765

第二题，请注意在逻辑链的建立上有一个非常明显的“空缺”，这个空缺就是这道题的关键：
从number of spending bill vote（因）到spend more taxpayer dollars（果），中间有一个非常明显的“空缺”。在assumption题中，这个空缺就是assumption：assume each bill vote are same amount。A选项相当于对Assumption直接取非。我对A的正确性无异议。
但是我觉得D也可以作为一个条件添加到“空缺”中从而对结论产生影响。条件1他们vote spending bill比较多+条件2但他们vote的那些spending Bill都是花他们自己的钱，结论就是“他们花自己钱比较多”，这个结论显然是对“他们花纳税人钱比较多”这个结论的有效削弱。
请指正。

jingliu097

alzn2765 发表于 2015-6-7 14:44
第二题，请注意在逻辑链的建立上有一个非常明显的“空缺”，这个空缺就是这道题的关键：
从number of spend ...

还是那句话，因果关系不找他因，你的想法是直接削弱了结论的，而不是逻辑。
其实我们并不知道X到底有没有花的比较多。

jingliu097

alzn2765 发表于 2015-6-7 14:26
谢谢你先！攒人品这么久，终于有人搭理我了

第一题，首先我们对题型的分类是一致的，果因。

我想了一下第一题应该是D
C可以说是其他动物得益于恐龙的灭亡，因为少了竞争，C有缺陷。
你是对的，C无关。

jingliu097

小问题，a could of？打错了吗

alzn2765

jingliu097 发表于 2015-6-7 15:50
还是那句话，因果关系不找他因，你的想法是直接削弱了结论的，而不是逻辑。
其实我们并不知道X到底有没有 ...

因果推理的其中一种削弱是找到一个前提，加到因果中间，使原来的因+新的条件，无法推导出原来的果。这有别与它因排除。比如：（前提）屋子下午刚刚打扫过，（结论）屋子现在现在一定是干净的。削弱：打扫那个人做的太卖力气干吐了。这个不是它因，这个额外的条件+原来的前提，无法得到原来的结论，达到了削弱的目的。
你再看看Helr逻辑法在因果推理的削弱/增强的方法总结那里，有我说的这个方法。
再说一遍，我不是提供它因。

alzn2765

jingliu097 发表于 2015-6-7 15:55
我想了一下第一题应该是D
C可以说是其他动物得益于恐龙的灭亡，因为少了竞争，C有缺陷。
你是对的，C无关 ...

感谢你认同我的观点！
但是，对于你对C错误的原因的解释我不认同。GMAT的削弱都是直接的条件直接作用于逻辑链产生削弱/增强结论的作用，而不可以通过选项给出的条件做出的二次推论来削弱。因为，从条件做出的推论往往都是必要条件而不是充要条件，也就是说从给出的条件可以推出不止一个推论，你无法保证条件一定产生你所希望的推论用来削弱结论。基于选项的二次推理都是错误的。

jingliu097

alzn2765 发表于 2015-6-7 18:44
因果推理的其中一种削弱是找到一个前提，加到因果中间，使原来的因+新的条件，无法推导出原来的果。这有 ...

但是如果选项中没有说明这是新的条件或者没有说明和原文的因有关系，就还是他因。
而且我觉得你这个例子有问题。