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# The owner of a four-storey commercial building discovered

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Re: CR: Termites and Exterminator [#permalink]

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02 Feb 2009, 13:10
IanStewart wrote:
B is the only real candidate among the answer choices, but I agree with icandy above - it really isn't a very good answer either. Why are we to assume that the exterminator's work didn't also affect the termites on the 4th floor? It's clear from the structure of the question that we are supposed to assume that, but the assumption doesn't seem warranted to me.

Thanks Ian. as you said, That is a pretty big assumption to be made. Thats why I found B ambiguous and chose D. D wasn't the best fit either. by POE, D But I guess GMAT wants you to think in a particular fashion when doing weaken Q's

grumpy,

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Re: CR: Termites and Exterminator [#permalink]

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02 Feb 2009, 13:53
Yes, B is correct -- no doubt about it. This is a fairly difficult question, but it is not at all ambiguous if you remember and apply three important principles:

(1) The correct answer to a Weaken question does not have to DISPROVE the argument; it only has to REDUCE the strength of the reasoning. (Similarly, the correct answer to a Strengthen question supports the reasoning, but does not have to PROVE that it is correct.)

(2) Given a cause-and-effect argument (i.e., an argument whose CONCLUSION states that A causes B), the most common way of weakening it is to show that another possible cause exists. (As noted above, it is NOT necessary to prove that this other cause was the actual cause. It is only necessary to show that the alternative exists and was not ruled out by anything in the argument.)

(3) Be specific and accurate in understanding what the conclusion and the evidence actually say.

For this question, start with the third principle: Understand exactly what the conclusion is. The question identifies the "effect" part of the cause-and-effect conclusion very specifically: The effect is the SPEED with which the termites on the first two floors were killed. The cause is "the exterminator's work", which means the act of pumping gas directly into the walls of those two floors. So the cause-and-effect conclusion is: Pumping gas directly into the walls of the first two floors caused the termites on those floors to die QUICKLY.

TAKE NOTE: The claim is NOT that the exterminators' action caused the bugs to DIE; the claim is that the action caused them to die QUICKLY.

Now to the second step: How do we weaken this claim? As the second principle indicates, we look for an answer which indicates that it was something ELSE, other than pumping gas directly into the walls, that caused the termites on floors 1 and 2 to die QUICKLY. Choice B does exactly this: On floor 4, where the gas was NOT pumped directly into the walls, the termites died just as quickly. At least on that floor, there must have been some other reason why they died so quickly -- and because that other reason existed on that floor, we cannot rule it the possibility that it was the real cause on floors 1 and 2. We do not know what that other cause could have been, and we do not need to: We DO know that it could not have been the act of pumping gas directly into the walls.

Choice D, as others have noted, strengthens the argument. It states that the speed with which the gas kills termites is (at least partly) inversely proportional to how far the gas must travel through the walls. We can logically deduce from this that, if other factors are equal, applying the gas at a place that is closer to the termites will cause them to die faster. This does not totally prove the conclusion, but it certainly supports it.
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Re: CR: Termites and Exterminator [#permalink]

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02 Feb 2009, 19:53
JohnLewis1980 wrote:
selvae, why do you drop D off?

Actually, the question relates with speed...

hey JohnLewis1980, sorry probably i assumed that D is self explanatory, since it is similar to C.

C - talks abt speed of killing increases if the concentration of exterminator's gas increases.
D - talks abt speed drop off sharply as the gas dissipates throughout the building's walls.

here we are not talking about the speed at which termites are killed. we need to prove tht speed at which the termites die is not only because of "The exterminator pumped gas directly into the walls on both the first and second floors. " but also by some other reason.

Hope you got it.
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Re: CR: Termites and Exterminator [#permalink]

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03 Feb 2009, 04:03
another B.........
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Re: CR: Termites and Exterminator [#permalink]

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03 Feb 2009, 06:01
grumpyoldman wrote:
Yes, B is correct -- no doubt about it. This is a fairly difficult question, but it is not at all ambiguous if you remember and apply three important principles:

(1) The correct answer to a Weaken question does not have to DISPROVE the argument; it only has to REDUCE the strength of the reasoning. (Similarly, the correct answer to a Strengthen question supports the reasoning, but does not have to PROVE that it is correct.)

(2) Given a cause-and-effect argument (i.e., an argument whose CONCLUSION states that A causes B), the most common way of weakening it is to show that another possible cause exists. (As noted above, it is NOT necessary to prove that this other cause was the actual cause. It is only necessary to show that the alternative exists and was not ruled out by anything in the argument.)

(3) Be specific and accurate in understanding what the conclusion and the evidence actually say.

Now to the second step: How do we weaken this claim? As the second principle indicates, we look for an answer which indicates that it was something ELSE, other than pumping gas directly into the walls, that caused the termites on floors 1 and 2 to die QUICKLY. Choice B does exactly this: On floor 4, where the gas was NOT pumped directly into the walls, the termites died just as quickly. At least on that floor, there must have been some other reason why they died so quickly -- and because that other reason existed on that floor, we cannot rule it the possibility that it was the real cause on floors 1 and 2. We do not know what that other cause could have been, and we do not need to: We DO know that it could not have been the act of pumping gas directly into the walls.

If I rephrase the argument in simpler language, using answer B as I do so, perhaps I can make clear why I think the question is badly constructed:

1) Without using B: "The exterminator showed up, did some work on floors 1+2, and the termites there died quickly. The exterminator's work was the cause."

2) Using B: "The exterminator showed up, did some work on floors 1+2, and not only did the termites there die quickly - so did the termites on the fourth floor. The exterminator's work was the cause."

In either case, there is a logical flaw - a post hoc ergo propter hoc fallacy. Just because the termites died after the exterminator showed up does not guarantee that the exterminator was the reason. Still, 2) is no less compelling an argument than 1); I don't find it any 'weaker'. It seems reasonable to think that gas can permeate the walls of a building quickly, so that work on lower floors affects termites on upper floors; it might also be that termites die when their queen dies, and the exterminator located the queen on the first floor and killed it. I have no idea - not my field. The question clearly intends for us to assume that work on the 1st+2nd floors could not affect termites on the 4th floor, and I don't see any grounds for making that assumption. Indeed, it seems implausible.

As you point out, when asked to weaken the conclusion in a cause-effect argument, "the most common way of weakening it is to show that another possible cause exists." Answer B does not suggest an alternative cause, or at the very least it's unclear whether B suggests an additional effect or an alternative cause. Were this a real GMAT question, the construction would be less ambiguous; the correct answer would allude to an alternative reason for the termites' demise, a reason which did not require any assumptions about how the extermination process works. That is, I'd expect the correct answer to read something like "A site analysis revealed that the walls throughout the building contain mercury residue, a substance which kills termites nearly instantly", or "Just before the arrival of the exterminator, a seismic disturbance produced vibrations in the walls of all of the buildings in the neighbourhood, and termites die quickly when exposed to vibration."

I certainly understand the rationale for choosing B, and it is the only answer choice that even warrants consideration; my only point is that a real GMAT would not contain such a question without including further clarification.
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Re: CR: Termites and Exterminator [#permalink]

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03 Feb 2009, 13:34
IanStewart wrote:
[ it might also be that termites die when their queen dies, and the exterminator located the queen on the first floor and killed it. I have no idea - not my field.

LMAO Very funny..
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Re: CR: Termites and Exterminator [#permalink]

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06 Feb 2009, 10:15
selvae wrote:
JohnLewis1980 wrote:
selvae, why do you drop D off?

Actually, the question relates with speed...

hey JohnLewis1980, sorry probably i assumed that D is self explanatory, since it is similar to C.

C - talks abt speed of killing increases if the concentration of exterminator's gas increases.
D - talks abt speed drop off sharply as the gas dissipates throughout the building's walls.

here we are not talking about the speed at which termites are killed. we need to prove tht speed at which the termites die is not only because of "The exterminator pumped gas directly into the walls on both the first and second floors. " but also by some other reason.

Hope you got it.

I'm afraid I don't

the question asks for something that undermines the validity of the explanation for the speed with which the termites were killed. For me, it's not asking for another reason that explains why termites were killed.

And for me, D perfectly undermines the reason of the speed at which the termites were killed, i.e. because as long as the gas enter the wall, its speed decreases...

What do you think?
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Re: CR: Termites and Exterminator [#permalink]

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08 Feb 2009, 23:09
ianstewart's rephrase actually changes the meaning of the argument, and partly misses the point as a result. With or without choice (B), he states the flaw as: "Just because the termites died after the exterminator showed up does not guarantee that the exterminator was the reason." Actually, the argument does not claim that the exterminator was the reason for the termites dying. It claims that the exterminator's ACTION (pumping gas directly into the walls of the FIRST TWO floors) was the reason for the termites on THOSE floors dying QUICKLY. This is a very different (and considerably more specific) claim.

Because this is a GMAT CR question, it is completely irrelevant whether or not it "seems reasonable" that work done on lower floors will affect termites on upper floors. This idea, or anything else that we might think is true in the real world, has nothing whatsoever to do with the question.

The question absolutely does NOT intend us to assume anything; none of these questions do. The question intends us to figure out what the ARGUMENT is assuming -- that is, what additional evidence would be needed, in addition to the evidence that is given, before we could prove the conclusion. For the purpose of answering the question, we act as if the evidence in the question is true; we don't CARE whether it is ACTUALLY true or not. We figure out what ELSE would have to be true ALSO in order to prove the conclusion. Then, because this is a Weaken question, we find the answer choice which contradicts or undermines that "what else".

In this case, we have a very common GMAT pattern: The conclusion is that A caused B, i.e., the pumping of gas directly into those walls caused the termites there to die QUICKLY. The evidence is merely that the one event preceded the other. (This is "post hoc ergo propter hoc", as ianstewart correctly says.) When this pattern (conclusion makes a causal claim, but evidence is mere correlation) occurs in the GMAT, the missing assumption is generally that there wasn't some OTHER cause.

It is true that in many GMAT Weaken questions of this type, the correct answer does provide another possible specific cause such as the examples that ianstewart gives. But this is not always the case. For example, the correct answer to question 88 on p. 493 of the "orange book" (GMAC Official Guide, 11th edition) is (E). That answer does not provide any specific other REASON why Sandactylus should have had blood vessels in its wings; it only says that other dinosaurs which did NOT flap their wings nevertheless DID have blood vessels in their wings. This is exactly parallel to answer choice (B) in this question, which says that other termites which were NOT located in the walls where the gas was pumped nevertheless DID die quickly.
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Re: CR: Termites and Exterminator   [#permalink] 08 Feb 2009, 23:09

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# The owner of a four-storey commercial building discovered

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