The owner of a four-storey commercial building discovered termites in

[color=#008000][b]Weaken argument:

B

Argu claims that due to ext term the termites killed "quickly" on first and second

If B, is true, how come the termites on fourth floor were "quickly" killed -so it undermines

On first scan, I overlooked word "quickly " in B

To weaken ( from Gmat CR Bible )

Cause --> Effect

(Exterminator efficiency) --> Killing

If we could hint any other cause , such argument is most weakened.

B shows a possibility of another cause.

Here is my take..

Termites on the floors were killed quickly because "The exterminator pumped gas directly into the walls on both the first and second floors. "

Now to undermines the validity of the explanation for the speed with which the termites were 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.

A, E - out of scope. we are not worried abt third floor infection/ The exterminator's gas pumping system works efficiently

C - talks abt the speed increase..but we are actually searching for another reason for speed other than "pumping gas directly into the walls"

D - talks abt speed drop off

B - clearly says that termites were killed in 4th floor even though the exterminator didn't pumped gas directly into the walls.

Hope it is succint.

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,

Are you listening? This is a kaplan Q.

Thanks

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.

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.

19. The owner of a four-story commercial building discovered termites in the building's first and second floors and called an exterminator. The Exterminator pumped gas into the walls on both the first and second floors. Due to the exterminator's work, the termites on those floors were killed quickly.

Which of the following, if true, most seriously undermines the validity of the explanation for the speed with which the termites were killed?

a. The third floor had no termite infestation.
b. Even though the exterminator did not pump gas into the walls of the fourth story, the previously undiscovered termites there died as quickly as they did on the first and second stories.
c. The speed at which termites are killed increases as the concentration of an exterminator's gas increases.
d. The speed with which the exterminator's gas kills termites drops off sharply as the gas dissipates throughout the building's walls.
e. The exterminator's gas-pumping system works efficiently even when pumping gas into both the first and second stories of the building simultaneously.


Alright, I am so struggling about on Number (B) that says "they did on the first and second stories." isn't that supposed to say first and second floors instead of saying stories.

I'm confused about they are saying stories and turned out saying floors. it just so confusing to me. Anyone can explain well.

I am highly doubtful between B and D.
B imples that there might be some other reason why the termites were dying, as the exterminator did not pump in gas on the 4th floor.
For D, if the killing power of the gas in dropping off sharply, when the gas is pumped through the wall, that too implies the termites ae not dying because of the gas.

Please explain!

Premises:
- Termites discovered on 1st and 2nd floors
- Exterminator pumped gas directly into the walls on 1st and 2nd floors.

Conclusion:
The termites on 1st and 2nd floors were killed quickly due to exterminator's work (pumping gas directly into the walls of these floors).

We need to weaken the explanation for the speed with which termites were killed. The argument says it was because the exterminator pumped gas directly into the walls of these floors.

Option (B) tells us that termites on 4th floor died at the same speed though the exterminator did not pump gas directly there. This brings into question that the termites of 1st and 2nd floors died quickly because the exterminator pumped gas directly there. Since the same reason was not present on 4th floor, it is possible that the termites died quickly because of some other common reason on all the floors. Hence (B) is the answer.



The reason you are getting confused with (D) is that you are taking info from (B) into account too. Else, (D) makes no sense. Forget option (B). Review the argument.

Premises:
- Termites discovered on 1st and 2nd floors
- Exterminator pumped gas directly into the walls on 1st and 2nd floors.

Conclusion:
The termites on 1st and 2nd floors were killed quickly due to exterminator's work (pumping gas directly into the walls of these floors).

D. The speed with which the exterminator's gas kills termites drops off sharply as the gas dissipates throughout the building's walls.

The exterminator pumped gas directly into walls of 1st and 2nd floors. That is where the termites died quickly. We are not concerned about what happens as the gas dissipates through all the walls of the building (presumably including the 3rd and 4th floors). We don't know anything about the pre or post exterminator status of 3rd and 4th floors. Hence, we are unable to weaken the argument using this option.

B clearly states that there was no correlation between the speed at which mites were killed and exterminator's work.

IMO B is right because - Though the Effect is present in the fourth story, the cause was not directly present there.

KAPLAN OFFICIAL EXPLANATION:

B

The conclusion here that the exterminator's work was responsible for the quick elimination of the termites is supported by the evidence that the exterminator pumped gas directly into the areas where the termites lived. The assumption is that the direct application of gas is faster than other means of extermination. To undermine the argument, lefs find the choice that calls this assumption into question.

Taken by itself, (A) is irrelevant. (C) and (D) appear to support, rather than weaken, the argument, because they suggest that a higher density of gas kills termites more rapidly (E) doesn't weaken the argument because it offers no information to help us compare the speed of termite deaths in gassed and non-gassed areas of the building. (B) is correct: The speed with which the termites in the first and second stories were killed is credited to the gas being injected into those areas. This explanation is weakened if termites are killed equally quickly on another floor, where no gas was injected.

Option D is nothing but a great distractor. It says that the speed with which termites get killed is inversely proportional to the speed with which the gases dissipate through the walls. Basically, it strengthens the argument that the trapping of gases in walls will help in killing the termites.

Option B is a clear winner, suggesting that there might be some other reasons because of which the termites died.

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