“GMAT逻辑解题方法 by lawyer ”一文的疑惑

stanfordvicky

此文解题步骤的第三大条的第4小条说：至此多数题能找到答案。有四类特殊的题型可用TEST去检验所选的是否正确或在剩下的几个混淆项中选出正确答案。分别是Assumption-Negation Justify-Justify FormulaEvaluate-Variance TestPoint at Issue-Disagree/Agree。


请问哪位可以把“Assumption-Negation Justify-Justify FormulaEvaluate-Variance TestPoint at Issue-Disagree/Agree“具体解释一下，并各举一例啊？不能体会不能体会个中含义啊，太深奥了。。。


谢谢

MissUindeed

sdcar2010 发表于 2011-3-4 11:41
For example, OG12-71Roland: The alarming fact is that 90 percent of the people in this country now r ...

sdcar2010，么么哒，说得真好～

kirajohn

及时雨！

nightingale

LS, when we say the argument still holds, you have to look at the argument in the whole, not just one aspect thereof.

When you negate A, as you did correctly, you get "Drivers who equip their vehicles with radar detectors are more likely to be ticketed for exceeding the speed limit than are drivers who do not." And this statement is consistent with one of the premise of the argument, therefore the argument still holds IF you follow the logic chain of the author because that's what the author claims! Whether or not the author's conclusion is right or wrong is not our concern for the assumption-type question. We have to treat the author's statements as correct. Since when you negate A, you do not weaken or refute the author's argument, the argument still holds.

-- by 会员 sdcar2010 (2011/3/5 21:01:45)

LS, Thanks for your explanation, but I am afraid I cannot agree.
To avoid duplicate discussion, pls see #5 here:
http://forum.chasedream.com/GMAT_CR/thread-524523-1-1.html

Thank you.

sdcar2010

LS, when we say the argument still holds, you have to look at the argument in the whole, not just one aspect thereof.

When you negate A, as you did correctly, you get "Drivers who equip their vehicles with radar detectors are more likely to be ticketed for exceeding the speed limit than are drivers who do not." And this statement is consistent with one of the premise of the argument, therefore the argument still holds IF you follow the logic chain of the author because that's what the author claims! Whether or not the author's conclusion is right or wrong is not our concern for the assumption-type question. We have to treat the author's statements as correct. Since when you negate A, you do not weaken or refute the author's argument, the argument still holds.

nightingale

OG12-78
A recent report determined that although only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors, 33 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. (using the assumption-negation method, conclusion still holds, but the thing is applying this method to the correct answer B, conclusion holds as well.urrrrr, this is killing me)
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. (so when i try to negate this choice, i change it to 'drivers who are ticketed for exceeding the speed limit less likely to exceed the speed limit regularly than are drivers who are not ticketed'. )

When you negate A, the conclusion still holds.

Let's negate B, as you did. Drivers who are ticketed for exceeding the speed limit are less likely to exceed the speed limit regularly than are drivers who are not ticketed. If this is true, then whoever are caught are not habitual fast drivers. Then 30% of those "ticket-earners" who have radar detectors are less likely to exceed the speed limit regularly.  This is in contrary to the conclusion "drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly."

You need to follow the logic chain and go forward until you can evaluate the impact on the conclusion.

-- by 会员 sdcar2010 (2011/3/4 11:54:30)

Sorry, I still do not understand here.

In my opinion, if you negate A, then drivers who equip their vehicles with radar detectors are more likely to be ticketed for exceeding the speed limit.  This is actually consistent with the facts stated in the question (the combined results from the fact that 33% vehicles ticketed are with radar detector while only 3% of drivers equipped their vehicles with radar detectors), so we cannot conclude that drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly.

I do not know whether I expressed myself clearly.  If not, pls tell.
Thank you.

stanfordvicky

thank you so much i got it have a good day ^.^

sdcar2010

The negation method never fails me for necessary assumption questions.  But you have to understand the logic of the argument and the meaning of the answer choices, including their opposite meanings.

sdcar2010

OG12-78
A recent report determined that although only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors, 33 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. (using the assumption-negation method, conclusion still holds, but the thing is applying this method to the correct answer B, conclusion holds as well.urrrrr, this is killing me)
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. (so when i try to negate this choice, i change it to 'drivers who are ticketed for exceeding the speed limit less likely to exceed the speed limit regularly than are drivers who are not ticketed'. )

When you negate A, the conclusion still holds.

Let's negate B, as you did. Drivers who are ticketed for exceeding the speed limit are less likely to exceed the speed limit regularly than are drivers who are not ticketed. If this is true, then whoever are caught are not habitual fast drivers. Then 30% of those "ticket-earners" who have radar detectors are less likely to exceed the speed limit regularly.  This is in contrary to the conclusion "drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly."

You need to follow the logic chain and go forward until you can evaluate the impact on the conclusion.

sdcar2010

For example, OG12-71
Roland: The alarming fact is that 90 percent of the people in this country now report that they know someone who is unemployed.
Sharon: But a normal, moderate level of unemployment is 5 percent, with one out of 20 workers unemployed. So at any given time if a person knows approximately 50 workers, one or more will very likely be unemployed.

Sharon’s argument relies on the assumption that

A) normal levels of unemployment are rarely exceeded [i think this is not right because if normal levels of unemployment are easily exceeded, then the conclusion that 'one or more will very likely be unemployed' still hold.]
B) unemployment is not normally concentrated in geographically isolated segments of the population [this is the right answer. however, i don't understand. when i apply the negation method, this choice does not matter to the assumption. say, if the unemployment is NORMALLY CONCENTRATED in geographically isolated segments of the population, the conclusion, which is 'one or more will very likely be unemployed', still holds, right? ]
C) the number of people who each know someone who is unemployed is always higher than 90 percent of the population
D) Roland is not consciously distorting the statistics he presents
E) knowledge that a personal acquaintance is unemployed generates more fear of losing one's job than does knowledge of unemployment statistics

- - - - - - - -  -- -

Roland hints that the unemployment rate is high since 90% people know someone is unemployed.

Sharon disagrees and claims it is normal for 90% people to know someone who is umemployed at a normal umemployment rate of 5%.

For necessary assumption questions, just use negation and see if that would cause the arugment to cumble.  If so, that answer choice is correct.  You do not need to worry why other choices are not assumptions other than that those wrong choices have no impact on the argument.

Let's negate B.
Unemployment is normally concentrated in geographically isolated segments of the population. If this is true, then certain area will have extremely high unemployment rate (let's say 10.5%) while other areas will have extremely low unemployment rate (let's say it is 0.5%). The national average for unemployment is still 5%. Then in the area with low unemployment, every 200 people will have one unemployed.  Then if one knows 50 people, it is likely that none of these 50 people are unemployed. Sharon's argument falls apart.