Logical reasoning PrepTest 124 · Section 3 · Question 4

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
An electric insect zapper killed 300 insects/day, only 12 of which were mosquitoes, so it won't help control that population.

Answer Anticipation:
There are two issues here.

First, This argument brings up some numbers, and whenever that happens, we should consider whether there's a Percent vs. Amount flaw. The premise is an amount—12 mosquitoes were killed. Is the conclusion about a percentage?

It doesn't specifically reference a percentage, but it does assume something about a percentage. When talking about controlling a population, the number of mosquitoes zapped is less important than what proportion of the population that represents. 12 seems low, but if there are only 20 mosquitoes in that area, then that might be enough to control the population. If there are 12,000 mosquitoes, not so much.

Since this question is asking us to weaken the argument, we should look for an answer supporting the idea that taking out 12 mosquitoes can help control the overall population, and so we should look for an answer helping to establish that 12 is actually a significant proportion of the overall population.

Second, the argument jumps from a premise about killing mosquitoes to a conclusion about controlling the mosquito population. If the bug zappers work to control the population in some way other than killing all the mosquitoes (e.g., scaring away remaining ones after a few don't come home), then the zappers might work despite the low body count. Any answer that brings up some other mechanism by which the zappers could work to drive mosquitoes away would also weaken this argument.

Answer Explanation:
This answer establishes that either the 12 mosquitoes killed were all the mosquitoes in the area, or the rest left after the bug zapper zapped the 12. This answer addresses both of the gaps in the argument, and so this is the correct answer.

Key Takeaway:
Sometimes, it's enough to get the general direction of the answer without needing to dig into the particulars of what impact it actually has on the argument. In this question, there were many answers that were too weak or a bit out of scope and thus had no impact on the argument, but they called the effectiveness of the zapper into question, which would align with the argument. Don't get too wrapped up in an answer like that—if it's generally in the wrong direction from the question stem, cut it without considering it further!

Incorrect. This answer is more or less restating what we already know—that 288/300 insects that the zapped killed weren't mosquitoes. This answer does expand that a bit by talking about what insects were attracted to the zapper, not killed by it, but that doesn't add much and, if anything, suggests that the zapper is better in controlling other insect populations. If anything, that aligns with the argument that it doesn't work to control mosquito populations.

Incorrect. Mosquitoes are harmful insects, so, if anything, this answer aligns with the conclusion. That said, since it talks about relative likelihood, it doesn't have enough logical force to address an argument about an absolute consideration—does the insect zapper zap enough mosquitoes to control that population?

Incorrect. The stimulus establishes that the zapper killed very few mosquitoes. If killing the other bugs would also help the mosquito population by removing predators, then the conclusion is stronger.

Incorrect. The stimulus itself never mentions attraction. It does, however, provide specific information about how many bugs were killed by the zapper. As such, this answer doesn't do much of anything to the argument. Again, if anything, by suggesting it's not 100% effective in killing insects, it would align with a conclusion about it being ineffective.