A recent test of an electric insect control device discovered that, of

Question

A recent test of an electric insect control device discovered that, of the more than 300 insects killed during one 24-hour period, only 12 were mosquitoes. Thus this type of device may kill many insects, but will not significantly aid in controlling the potentially dangerous mosquito population.

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

(A) A careful search discovered no live mosquitoes in the vicinity of the device after the test.
(B) A very large proportion of the insects that were attracted to the device were not mosquitoes.
(C) The device is more likely to kill beneficial insects than it is to kill harmful insects.
(D) Many of the insects that were killed by the device are mosquito-eating insects.
(E) The device does not succeed in killing all of the insects that it attracts.

daagh · Answer

The test after the using device showed no live mosquitoes, which indicates that the device did kill all the available mosquitoes. Perhaps the problem was because there were not enough mosquitoes on the site. Choice A makes this point clear and weakens the conclusion

XCDY · Answer

Sir,

The option D also weakens the argument. Why it cant be the answer?

YassiHASHMI · Answer

(D) Many of the insects that were killed by the device are mosquito-eating insects.

If many mosquito-eating insects are killed by the device, there will be less insects to eat mosquitos and hence, mosquito population will be maintained/increased. So I think D strengthens the argument - not the answer.

Posted from my mobile device

prateekchugh · Answer

KAPLAN OFFICIAL EXPLANATION

(A) Weaken the Argument 
In most cases, a weakener will directly challenge a central assumption.
We’re asked to weaken an argument regarding the results of testing an electronic insect control device. The author concludes (note the keyword “thus”) that the device may kill lots of insects, but won’t help control the mosquito population. That prediction is based on the mere 12 mosquitoes counted among the more than 300 insects killed within a 240 hour period . Well, that’s a pretty strong prediction to be based on such paltry evidence. To justify such a prediction, the author must take for granted that the device left many mosquitoes unharmed. After all, if there were only 12 mosquitoes to start, then the device works quite well, doesn’t it? The author’s assumption is severely discredited by  (A) , which suggests that the device killed – or at least repelled – all the mosquitoes in the vicinity, making it quite successful in controlling the mosquito population.

(B)  If the vast majority of the bugs attracted to the device were not mosquitoes, then the device may not be so effective at controlling the mosquito population. But again, the argument will be strengthened or weakened by information concerning the proportion of mosquitoes killed by the device.  (B)  does not provide such information.

(C)  Beneficial insects vs. harmful insects? This is a distinction that doesn’t affect the argument in the slightest.

(D)  If many of the insects killed by the device usually eat mosquitoes, then there might be more mosquitoes left with less of their predators around. Thus  (D)  could strengthen the argument, which we definitely don’t want.

(E)  is nowhere near specific enough. In order to know how strong or weak the argument is, we need to know whether the device succeeds in killing all of the mosquitoes it attracts.

rounakkedia172 · Answer

GMATNinja   VeritasKarishma   daagh

From the stats provided above, we can say that 12/300 = 4% of the insects killed were mosquitos.
In B, If a very large proportion were not mosquitos isn't this statement the weakener? 
If 99% of the population were not mosquitos, it killed 4x.

Or, the choice is incorrect because a very proportion can also mean 90% then it is strengthening the conclusion.

Please confirm. Thanks.

CrackverbalGMAT · Answer

Pre-thinking:

Conclusion:  The device will not aid in controlling the mosquito population.

Premises on which it is based:  A test of the device discovered that, of the more than 300 insects killed during one 24-hour period, only 12 were mosquitoes.

Since the proportion of mosquitoes killed is low, the stimulus argues that the device is ineffective in killing mosquitoes. We are asked to weaken the conclusion. Therefore we are looking to rule out alternate explanations, reverse causality or correlation. One possible alternate explanation could be that there are already very few mosquitoes, which is what caused the proportion of mosquitoes killed to be low.

Let us examine the answer options:

(A) A careful search discovered no live mosquitoes in the vicinity of the device after the test.  Correct answer. Since there are no live mosquitoes nearby, it is possible that all available mosquitoes are killed by the device, which reinforces the claim that there were only few mosquitoes to begin with.

(B) A very large proportion of the insects that were attracted to the device were not mosquitoes.  We are concerned not with the insects "attracted" to the device but with the insects "killed" by the device. Eliminate.

(C) The device is more likely to kill beneficial insects than it is to kill harmful insects.  This option does not address mosquitoes at all, since we do not know which insects are beneficial and which are harmful. Eliminate.

(D) Many of the insects that were killed by the device are mosquito-eating insects.  While this could be a possible explanation for why only few mosquitoes were killed, the link is tenuous at best. Option (A) is a much more direct explanation.

(E) The device does not succeed in killing all of the insects that it attracts.  We are not concerned with the proportion of all insects killed. Eliminate.

Hope this helps.

VerbalBot · Answer

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