Critical Reasoning

Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?

the answer is e..since this is a causation, to find a weakener, we need to find an answer that the same effect is not caused by the same cause.
cause -- overcrowding in schools --- A
effect -- decline in reading --- B
answer choice D says A causes not B.
answer choice E says not A causes B.
Only E says tht something else is causing B.
choice D doesn't weaken.

adam007 wrote:Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?

Its very easy:
we have to read the statement in this way to find out the answer:
"Overcrowding in the schools results in decline of reading skills"

Now, in order to weaken the statement we should look for the option which states, "overcrowding doesnot result in decline of reading skills".

So, if you read all the options, you will see that E is perfect fit.

adam007 wrote:Can somebody please be so kind as to explain me why the ans is E and not D (example comes from Kaplan's GMAT 800 - but I still don't get the explanation).

Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools.

Which of the following, if true, most seriously weakens the argument above?

A. The high school system in Gotham succeeds in giving students a good education at considerably less cost than do most systems.

B. Several cities have found that overcrowding in the schools is not always associated with lower reading scores.

C. Gotham schools have a greater teacher-to-student ratio than most other school systems.

D. Students' reading skills have not declined in other cities where the high schools are just as overcrowded as those of Gotham.

E. Schools are not overcrowded in many cities where high school reading scores have declined more than they have in Gotham.

Why E??? For me it's clearly D because:
1) it offers alternative explanation (there must be some other reason for decline in reading skills than overcrowded schools)
2) E talks about "scores" not "skills" - isn't it a shift of scope?

There are, most commonly, 2 different types of correct answers we see for "weaken the causation argument" question. Either:

(1) an alternative cause; or

(2) a disconnect between the proposed cause and effect.

Rarely, we see a 3rd type of right answer:

(3) a suggestion that the author has cause and effect reversed.

It's always a good idea to predict the right answer for assumption, strengthening and weakening questions. Predicting helps you to find the right answer more quickly and, perhaps more importantly, prevents you from being distracted by the wrong answers.

In this question, our prediction may have been something like:

Either another reason why reading skills have steadily declined OR something that suggests that reading skills and overcrowding are not connected.

Only (e) matches either of those predictions: it disconnects the cause (overcrowding) from the effect (declining reading skills) by telling us that there are lots of other places where the cause is present by the effect is absent.

(d), on the other hand, tells us that we can still get the effect without the cause. This is not an effective rebuttal to a cause-effect relationship, since it doesn't propose any alternative reason why skills have declined.

Let's look at a simpler, yet analagous, argument:

John just caught the flu, which can only be the result of all the time he spends in the emergency room at the hospital.

(d) Lots of people catch the flu even though they never visit the emergency room.

(e) John's co-workers, who also spend lots of time in the emergency room, didn't catch the flu.

Here, (e) clearly makes us doubt that John caught the flu in the ER - after all, if the ER was where he caught it, then we'd expect some of his coworkers to have it too.

(d) doesn't make us doubt the argument at all - just because there are other ways to catch the flu doesn't mean that the ER isn't a likely spot to pick it up.

Nikhil, Stuart - thank you very much! Very helpful!

Thanks. Nikhil

according to CR bible, we can weaken by showing that

a, cause exist, effect dose not exist

b, cause dose not exist, effect exist

D is a, and E is b, so both D and E is correct.

Stuart, I think this question is wrong

duongthang wrote:according to CR bible, we can weaken by showing that

a, cause exist, effect dose not exist

b, cause dose not exist, effect exist

D is a, and E is b, so both D and E is correct.

Stuart, I think this question is wrong

First, let me point out that just because something is called a "bible" doesn't mean that it's always correct!

Second, it's very important to understand how to apply the information you get about the test; a little bit of information can be bad for your score if you misuse it.

In this question, we have the very strong conclusion "which can only be the result of overcrowding in the schools".

In other words, the author is dismissing all other possible causes.

(E) directly refutes this by showing that there can be other causes for overcrowding.

(D) does not refute this; the author doesn't state that overcrowding always leads to poor reading skills, just that it did so in this particular case.

Stuart,

According to Critical Reasoning Bible, when a GMAT quesion concludes that A CAUSE B, the question is concluding that ONLY A CAUSE B.This is discussed very clearly in the Bible.

and because ONLY A CAUSE B, (no A, B exist) and (A exist, B do not exists) both are weakener.

that is why both D and E in the question are correct. and the queston is wrong.



Kaplan book is excellent saying that weakening and strenthening is increasing doubt and trust.However, Kaplan book has an error.

However, Kaplan book is wrong saying that negation of assumption "make conclusion fall apart". NO,it is good enough that negation of assumption is weakening the conclusion, not necessarily destroying conclusion.Negation of assumption is an weakner or destroyer, and negation of weakener is an assumption.

this mistake of Kaplan book confuses me a long time.

Hi Stuart,

Ain't ur concept and ans. contradictory ?

Ur ques.:
John just caught the flu, which can only be the result of all the time he spends in the emergency room at the hospital.
(d) Lots of people catch the flu even though they never visit the emergency room.

(e) John's co-workers, who also spend lots of time in the emergency room, didn't catch the flu.

A causes B. But to say B can be caused only by A, there should be no other reason that can cause B.

Here, as stated cause of flu can only be the result of all the time he spends in the emergency room hence it says time in ER is the only cause.
If I prove that there is some other cause of flu, I can surely weaken the statement. D does exactly this. As there are people who caught flu even when they never visited ER, we can safely say that assumption is wrong.

Isn't it?

Hi Staurt

Why B is not the answer and E is as B also says there is another cause for lower reading scores

kaplan explanation says (B)and (D) point to overcrowding without declining skills how this is true since lower reading scores also means declining skills

Stuart,

Thanks man! the explanation makes sense...


@duongthang :

No offenses! But "euphemism" is the advice for you. If you know what I mean.

Anyway, as Stuart has already said, quoting "bible" in every response does not make any statement/explanation/counter argument correct. In fact, as you must already be aware that in GMAT, no response is absolutely correct or absolutely wrong. It's just that the credit response is, in some way, least "bad" or somewhat better among the choices. Also, a question doesn't become "wrong" if has two answer choices which appear to be true. It's your judgment/wisdom in the end which will help you pick the credit response.

Now, as you only understand biblical language, I'm sure that you have mugged up the primary objectives while solving a CR question? No? Please revise them before you start applying the book's technique.

For your reference, "Weakening" type is the third family, for which rule # 2 says :

"The answer choices are accepted as given, even if they include "new" information. Your task is to determine which answer choice best attacks the argument in the stimulus"

Further, bible says : When evaluating an answer, ask yourself, "Would this answer choice make the author reconsider his/her position ?

If option D is true, the author would still think "Hmmm..... Maybe overcrowding can be one of the reason for declining reading skills, as seen in Gotham" and would not take his words back.

If option E is true, the author would definitely have to take his argument back, as this option shows that there is no relationship between declining reading skills and overcrowding.

Following orders of "The Bible", you will have to pick E !

Hope I'm clear enough!

We have to prove Overcrowding is causing decline in reading skills

E says Not Overcrowding but something else is causing Decline Reading Skill so E is correct
B says lower reading scores are not always due to OC so there must be some other cause of lower reading scores Why B is wrong? it does the same thing as E

Also Is D incorrect because we have to prove that decline can be of anything other than overcrowding wherease in D we donot have a decline

Why B is wrong and is D wrong because in D we donot have a decline

vaibhav.iit2002 wrote:Hi Stuart,

Ain't ur concept and ans. contradictory ?

Ur ques.:
John just caught the flu, which can only be the result of all the time he spends in the emergency room at the hospital.
(d) Lots of people catch the flu even though they never visit the emergency room.

(e) John's co-workers, who also spend lots of time in the emergency room, didn't catch the flu.

A causes B. But to say B can be caused only by A, there should be no other reason that can cause B.

Here, as stated cause of flu can only be the result of all the time he spends in the emergency room hence it says time in ER is the only cause.
If I prove that there is some other cause of flu, I can surely weaken the statement. D does exactly this. As there are people who caught flu even when they never visited ER, we can safely say that assumption is wrong.

Isn't it?

I agree ...
experts please re-open this question ...this needs further discussion

Let me just first to say that this is a pretty difficult discussion to sort through, so I won't try. However, I appreciate the need for clarity on the general issue. Stuart's explanation is the only truly important one: the way to properly predict the answers. However, I must refute the following, allegedly from the CR Bible:

duongthang wrote:according to CR bible, we can weaken by showing that

a, cause exist, effect dose not exist

b, cause dose not exist, effect exist

This is not true. Most causation is what is called, in formal logic, "Necessary Causation." This means that, if A-->B, A is necessary for B to occur. However, it does NOT mean that A is always sufficient for B to occur. For example, take this sentence:

"Dangerous additives to pet food caused a number of pets in the U.S. to die last year."

If you see this on the GMAT, it means that the dangerous additives were necessary, so that without them, pets wouldn't have died. This is the same as saying "ONLY the additives caused the pets to die." However, it does NOT mean that the additives ALONE were to blame. In fact, there are of course other contiguous causes, such as the fact that the pets had to eat the food.

Therefore, it DOES weaken a Causal Argument to say that C-->B, because it shows that A wasn't necessary, and therefore wasn't necessarily the cause:

"A dangerous flu affecting dogs and cats spread throughout the U.S. last year."

Similarly, we can show "effect without cause" to Weaken:

"The same number of pets died the previous year, when there were no tainted foods."

However, it does NOT weaken the argument to show that an additional causes was needed alongside the initial cause:

"The dangerous additives needed to be mixed with tap water to become dangerous, and the U.S. is one of the few countries in the world where residents regularly use tap instead of bottled water."

This does NOT weaken the argument, because the additives, although now clearly insufficient on their own, are STILL likely a necessary cause of the pet death. Similarly, "cause without effect" is actually NOT a weakener!

"The same additives were present in dog food throughout India, yet no inordinate number of pets died there last year" -- NOT A WEAKENER!

This is formal logic, which rarely appears on the GMAT, but it is a valid and important distinction between necessity and sufficiency, which are easy to confuse but are in fact quite different. And that is why, in the original question from long ago, the answer is (E), and not (D).

So, regardless of what you've read, learn this once and for all:

Cause-without-effect IS NOT a Weakener. Effect-without-cause IS a Weakener.

Finally, I want to address this point, as it's been made in this thread:

duongthang wrote:However, Kaplan book is wrong saying that negation of assumption "make conclusion fall apart". NO,it is good enough that negation of assumption is weakening the conclusion, not necessarily destroying conclusion.Negation of assumption is an weakner or destroyer, and negation of weakener is an assumption.

This is incorrect. The GMAT is testing necessary assumptions. That's why they always say something like, "Which of the following is an assumption on which the argument above depends?" As we've just learned, a necessary assumption is something without-which-not. That is why the Negation Test or Denial Test or whatever you want to call it works so well on Assumptions, albeit no other question type. If an Assumption is truly necessary to the Argument, then its negation must totally destroy the argument -- just as a necessary cause, if present without the effect, destroys the argument in favor of causation.

Hope that makes things a little clearer with regards to necessity and sufficiency in GMAT Causation!