Critical Reasoning

welocome:) i had bombed it completly:(

uptowngirl92 wrote:Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following would it be most important to ascertain in evaluating the argument?

(A) Whether populations of the other species on which deer tick larvae feed are found only in the areas also inhabited by white-footed mice.
(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
(C) Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice.
(D) Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed.
(E) Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans.

I agree that (B) is the correct answer to the question (and, as always on the GMAT, not just the "best" answer, but the only answer that satisfies the question).

Relevant information questions (of which this is one) are really scope questions. The question could have read "which of the following is most inside the scope of the argument" or "is most closely related to the author's central assumption".

Another way of thinking about relevant information questions is as hybrid strengthen/weaken questions. The correct answer is a question that, if you get one answer, would strengthen the argument; if you get the opposite answer, it would weaken the argument.

Let's take a look at the choices previously discussed:


(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.

If the answer is yes, the size of the deer tick population is currently limited by the availability of food sources, then the conclusion is weakened - an increase in food sources would likely just lead to an increase in deer ticks, not a spreading out of deer ticks to these other animals.

If the answer is no, the size of the tick population isn't currently limited by the availablity of food sources, then the conclusion is strengthened - the same number of ticks spread out over more animals, a higher proportion of which are uninfected, means that fewer deer ticks will be exposed to the bacterium.

Note that neither answer proves or disproves the conclusion (e.g. we don't know for sure if deer ticks will spread out to other animals), but that's not our task - we just want the choice that's most relevant.

Next choice:

(A) Whether populations of the other species on which deer tick larvae feed are found only in the areas also inhabited by white-footed mice. [emphasis mine]

Do we really care if that's the only place that these other species are found? No - we just care that it's at least one place that the other species are found.

If these populations are found other places as well it would certainly affect the amount of impact that their propogation has on infected ticks, but not whether there's an impact on the infected ticks, which is what the argument is about.

Finally:

(D) Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed.

Wuzzat? This might be relevant to the general issue about how ticks get infected, but we know nothing at all about the life cycle of the tick - as soon as we see "become infected as adults" we should eliminate this as outside the scope (especially because it has nothing to do with the food sources of larvae).

Testluv and Stuart, thanks for the clear explanation!
I confirm, I found the question in Gmatpret test, the OA is B.

Testluv wrote:Hi uptowngirl92,

thanks a lot. Haven't seen this question before, unfortunately...the OA (which, by the way, I think you forgot to post!) is in contention?

Well, choices A and D are the only other two choices I seriously considered. In an evaluate the argument question, oftentimes the best way to evaluate the potential relevance of an answer choice is to think about the answer choice at its extremes, and then to compare the extremes to the argument (which needs to be kept clear in your head).

Applying this to choice A: if the safe species are not found in areas where there are no mice, there is no problem because there are no mice, and if they are found in mice-having as well as non-mice-having areas, again, there is no problem. In both cases, there is no obvious reason for thinking that the plan's chances will be hurt.

choice D: if an uninfected adult deer tick can pick up the disease by eating the deer on which infected larval deert ticks fed on, then that problem exists whether or not we implement the plan argued for by the author.

I posted above as to why I think the OA should be B....I do hope that helps, I know this is a tough and confusing question!

@testluv
OA is B...... That was a very good explaination.

Thanks

IMO B

why B why can't E .

the central point is the transmission of bacteria . size of the deer tick is irrelevant what matter is the number of ticks that have picked up the bacteria while feeding .

E is someway related to the transmission of the bacteria .

I did come across this question on GMAT prep.

The OA to the above problem is (B)