Lyme disease is caused by a bacterium transmitted to humans by deer ti

Hi zoezhuyan,

Wow, this is a tricky one! It's super easy to get caught up in the complex wording here, so let's break this down in a simple way. Here's what the argument is saying: Ticks pick up the bacterium by feeding on infected whitefooted mice. However, ticks can also feed on other animals. So if the population of those other animals is increased, ticks will feed on a lower percentage of infected mice, and therefore will pick up bacteria at a lower rate -- i.e., fewer ticks will acquire the bacterium. The deer ticks that are already infected will stay infected, but this argument is talking about newly infected ticks -- the ticks that will become infected in the future. The "infection" is an ongoing action; each day, larvae are feeding on mice, and some of them are becoming infected.

Let's say there are 10 ticks, and each one feeds on one animal each day. If there are 100 whitefooted mice around, and basically no other animals that the ticks like to feed on, the ticks will all be feeding on the whitefooted mice, and so could all pick up the bacterium. But now, let's say we add in 900 other animals that the ticks also can feed on. Each tick, then, only has a 1 in 10 chance of feeding on a mouse which might be infected. So we would instead assume that only one out of the ten ticks might pick up the bacterium (on a given day).

Now of course, this argument rests on a number of assumptions, which are what we need to identify in order to answer this question. One assumption, for example, is that the tick population will stay unchanged (e.g. 10 ticks). If instead, with all this extra food around, the tick population starts to grow proportionally, the argument will break down. If the population grows to 100 ticks, there will be just as many ticks acquiring the bacterium as before (10).

This assumption is exactly what's being addressed in (B). It says:

(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.

So if we know whether there are already more than enough animals for the ticks to feed on, we will be able to predict whether the tick population will start growing if new animals are introduced. That will help us evaluate the argument.

Several of the other answer choices are tempting, but don't address a direct assumption that the argument rests on, and that's the key to these types of questions

I hope that helps!
-Carolyn

MagooshExpert
Thanks Carolyn

Appreciate your awesome explanation

Easier than other explanation for me to understand.

And I did realize it's far away to finish my GMAT journey.

Regarding this question,
I did not completely get what the meaning of "number" in conclusion, merely interpreting that number is integer value, like one, two, three,
I totally did not get that it sates a possibility that ticks will become infected.

is the misunderstanding hard to improve in few months for an non-native?

I know assumption is important key for CR questions, especially essential assumption,
so far, I am not good at assumption, sometime, I even have no idea before diving into answer choices,

I am keen to improve interpretation and assumption
any advice ?


Thanks again

Have a nice day
>_~

Hi zoezhuyan,

Interpreting phrases like this is definitely tricky. I think the key here is the word "acquiring":

the number of ticks acquiring the bacterium would likely decline.

The tense of "acquiring" implies a continuous action, which tells us that this is a process that is ongoing (and will continue into the future). If it instead said "had acquired", then that would imply that the ticks had already acquired the bacterium, and that's something that just happened in the past, not the future.

Misunderstanding complex questions and statements like this is definitely a very common problem, especially for non-native speakers. But don't worry, there are definitely ways you can improve! Please see these articles for lots of our tips and suggestions:

• GMAT for Non-Native English Speakers
• GMAT Verbal for Non-Native English Speakers
• Arguments and Assumptions on the GMAT
• More on Assumption Questions
• Assumptions and the Negation Test
• Active Reading -- Increase Your Understanding
• Find the Conclusion or Inference
• The Parts of an Argument
• Evaluate the Argument

I hope some of that is helpful!
-Carolyn

Hi mikemcgarry, GMATNinjaTwo, GMATNinja, MagooshExpert Carolyn, @sayantanc2,@VeritasPrepKarishma,

I reviewed this question today,
I can understand the previous explanation why B is correct,
But I still have no idea my reasoning of A and D is incorrect, i picked up A and confused by D, that means i have bugs in my reasoning, i genuinely want to find out the bugs.
Would you please help point out?

Thanks tons
Have a nice day
>_~

Hi zoezhuyan,

It looks like others have previously explained why the other answer choices are incorrect. Could you explain a little bit more about what (in those explanations) you're still having trouble understanding, and explain your thought process for these answer choices a bit more? Then we can try and identify those bugs

-Carolyn

Hi MagooshExpert, yes, others have previously explained why other answer choices are incorrect,
When i reviewed this question, i am lost in my own reasoning , and i have no idea what's bugs in my rasoning, i geniunely need your help fingue out the bugs.

as per 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.

I picked up this one.
here is my reasoning:
I did not neglect "ONLY", but i don't think ONLY will be a solid reason to eliminate
If the certain species live in the same place as the mice live, implying there are food without bacterium for larvae, except mice. so maybe there are other factors that larvae feed mice rather than lack of certain species.
if the certain species are found other place where mice don't live, then introducing uninfected species will provide the food for larvae, making the conclusion more likely.

That's why i picked it up earlier.

BTW, the opposite of "ONLY" is "NOT ONLY", if species live in place A, the opposite is the spices live in any place except place A , right?

as per (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.


This one, many explanations say it is irrelevant.
seems i did not get why irrelevant, although i did not choose it.

If the deer ticks will become to carry bacterium even though they were uninfected at larvae stage, then, introducing certain species does not work.
If the deer ticks will not become to carry bacterium even though they were uninfected at larvae stage, then, introducing certain species would expand the food source for larvae, it helps the conclusion.

mikemcgarry, GMATNinjaTwo, GMATNinja, MagooshExpert Carolyn,sayantanc2, VeritasPrepKarishma

Appreciate your clarification.

Thanks in advance
Have a nice day

>_~

Hi zoezhuyan,

Thanks so much for the details! That's really helpful

Let's look at A first. First of all, the opposite of ONLY is NOT ONLY, but it looks like you may be confusing what that means. If we have this statement:

That species lives only in place A

The opposite of that statement is:

That species does not only live in place A

That means that the species could be found BOTH in place A AND outside place A. So negating the statement just means that there is no longer a restriction on where the species lives, so it still could live in place A. That's why choice A doesn't work here -- knowing whether the other species are only in the areas with the mice or not doesn't help us evaluate the argument. If those other species are not only in the areas with mice, that doesn't mean they are NOT in those areas, just that they are not ONLY in those areas, which is very different. Knowing that information doesn't help determine the effect on the tick population.

For option D, knowing whether the ticks can be infected as adults doesn't actually affect the argument. If the ticks can be infected as adults, then introducing the other species that don't carry the bacterium will still result in a decrease in infected ticks. That's because there will now be fewer animals that carry the bacterium, so whether the ticks encounter them as larvae or as adults, there are fewer that will carry the bacterium, and therefore the number infected would decline. The stage when the ticks actually get the bacterium doesn't matter.

Does that help clear things up? If not, let me know!
-Carolyn

Thanks so much Carolyn, MagooshExpert

I got it, great helpful.

AS per D,
I understand your explanation, I have a further question,
the number will decrease in short term after introducing the other species that don't carry the bacterium,
but in long term,if it is true those deer ticks that were not infected as larvae can become infected as adults, then the number will increase,
Does it mean introducing does not work ultimately?

Please help.

Thanks in advance.

Have a nice day
>_~

It looks like MagooshExpert Carolyn has already done a fantastic job explaining this one, but I'll add my two cents...


Notice the word "if" in the conclusion: "...if the population of these other species were increased." The conclusion involves a hypothetical situation. It doesn't matter where those other species are currently found. Assuming we can increase the populations of those other species, will the number of ticks acquiring the bacterium decline? (A) has no bearing on the argument and can be eliminated.


We are told that, "Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected whitefooted mice." Sure, it might be possible for deer ticks to become infected as adults. And increasing the populations of the "certain other species on which the larvae feed" will not help reduce this type of infection.

But deer ticks GENERALLY pick up the bacterium while in the larval stage. So if we can substantially reduce the number of ticks that pick up the bacterium in the larval stage, then that should surely reduce the number of infected ticks. The fact that it is still POSSIBLE for ticks to become infected doesn't matter. We aren't trying to ERADICATE the disease. We are simply trying to reduce the number of infected ticks. That is why (D) is irrelevant.

I hope that helps!

Hi, GMATNinja
Wow~~ Great point
I did negelect it

I think i know where i made a mistake, maybe D will affect the effect of the plan if D is true, leading the effect not as perfect as expect, but the plan still can work.

Thanks very much.
Have a nice day
>_~

Hello GMATNinja,

Would you please help in understanding the verbiage of the phrase used in B- X is limited by Y? Being a non native speaker, I have difficulty in deciphering the linguistic aspect of the mentioned phrase.

Thank you.

Sure thing, TaN1213. If we say that X is limited by Y, then we mean that Y is restricting X or otherwise holding back X.

This can be a quantitative restriction, e.g.:

• "Our vaccination program is limited by the number of volunteers we can train."
• "Admissions are limited by the number of open seats."

This can also be qualitative or abstract constraint, e.g.:

• "His appetite is limited by his desire to lose weight."
• "Her imagination is limited by the dull curriculum taught by her GMAT tutor."

Going back to choice (B), let's simplify:

• the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on
• the size of the population is currently limited by the availability of animals for the tick's larval stage
• the size of the population is limited by the availability of animals

In other words: tick population size is restricted by how many animals are available for them to eat.

I hope this helps!

I read over and over again but cannot get how other safe animals relate to already infected ticks...
Question asks whether a decline in number of deer ticks acquiring bacteria happens. In case B, I suppose the infected deer tick population stays stable since other animals, who do not host infection, do not necessarily reduce the existing infected deer tick population IMO. If the question asks whether infected deer tick pop kept controlled, it would make sense.

I think your YES/NO analysis is a bit erroneous. sayantanc2k
Conclusion - If 'other species' is increased , the number of infected deer ticks will decline and the number of people contracting Lyme disease—would likely decline.

First consider option B:
When Yes: Size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.

Then the conclusion is HELPED. Increasing the other species will help. If 'other species' is increased , the number of infected deer ticks will decline and the number of people contracting Lyme disease—would likely decline.

WHen NO :- Size of the deer tick population is currently NOT limited by the availability of animals for the tick's larval stage to feed on.
It means deer tick population already has enough food. Introducing other species wont help much.
The conclusion "If 'other species' is increased , the number of infected deer ticks will decline and the number of people contracting Lyme disease—would likely decline" can not follow.
The conclusion gets HURT.

So option B is correct.

VeritasKarishma

GMATNinja

Is my explanation correct ?

Bacteria -> whitefooted mice -> larvae of deer ticks -> humans

Larvae feed on other species (other than white footed mice) too which do not harbor the bacterium so increase the population of these other species. Fewer people will get Lyme disease.

Here is what the argument seems to be saying - Larvae feed on infected white footed mice and other species (say black footed mice and yellow footed rats!!). If the population of there species is increased, the larvae will have more availability of non infected food and hence fewer larvae may get infected with the bacteria. Hence, fewer people will catch lyme disease.

We need useful to evaluate option - an option that will help in determining whether this will actually happen. Whether introducing more number of other species will lead to fewer larvae getting infected with the bacteria.

A. Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white footed mice.

Yes, other species are found only in areas which have white footed mice - Then it seems that only these areas have infected larvae since only they have the food source. Introducing more number of other species should reduce infected larvae.
No, other species are found in areas without white footed mice too - These other areas have uninfected larvae so no need to introduce more number fo other species. But we should introduce more number of other species in the areas where we find both white footed mice and other species. It might help reduce the number of infected larvae.
This option just helps in evaluating where we should introduce more members of other species. It doesn't say whether our plan is likely to succeed or not.


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

Yes, size of larvae population is limited by food availability - Say we have 100 larvae every season - 50 feed on white footed mice and 50 on other species. If we introduce more food (other species), the number of larvae might increase to 200. 50 may still feed on white footed mice while 150 feed on other species now since more number of other species are available. Did the number of infected larvae go down? No, that number may not go down.

No, the size of population is not limited by food. There are and will be 100 larvae only no matter how much food is available. Now, if more number of other species are available, 25 larvae might end up feeding on white footed mice while 75 might end up feeding on other species since percentage of other species in the overall food has increased.

Hence this option does help in evaluating whether the plan will succeed or not.

C. Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white footed mice.

Another plan is out of scope. We need to look at the probability of success of THIS plan.

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.

Again, irrelevant. What happens to deer ticks not infected at larvae stage is irrelevant. The argument clearly says "generally ticks pick up the bacterium while in the larval stage..." (say this happens in 90% cases of infected ticks). There could be other ways in which they pick up bacteria too (say in 10% cases) but we don't need to worry about those. We are trying to reduce the number of ticks that pick up bacteria at larval stage by feeding on white footed mice. That will bring the overall number of infected ticks down and hence reduce the number of people infected with lyme disease.

E. Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmits to humans.

Other bacteria and other disease are out of scope.

Answer (B)

Hi Maa'm,

Can we explain that option A is wrong , using "variance" technique ?


The conclusion is :- "Larvae feed on infected white footed mice and other species (say black footed mice and yellow footed rats!!). If the population of these species is increased, the larvae will have more availability of non infected food and hence fewer larvae may get infected with the bacteria. Hence, fewer people will catch lyme disease. "

Option A says --- "Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white footed mice."

Yes...--> "Populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white footed mice." Then if the larvae now have two options and fewer larvae will feed on infected mice and the conclusion that " If the population of these species is increased, the larvae will have more availability of non infected food and hence fewer larvae may get infected with the bacteria. Hence, fewer people will catch lyme disease. " can follow. The conclusion is HELPED.

No---> "Populations of the other species on which deer tick larvae feed are found NOT only in areas also inhabited by white footed mice."
Then it means non-infected species are found both in areas inhabited by white-footed mice and other areas. So if the population of other , non-infected species is increased , then obviously the larvae will have more availability of non infected food and hence fewer larvae may get infected with the bacteria. Hence, fewer people will catch lyme disease. The conclusion is HELPED again.

Both YES and NO scenarios are "HELP"ing the conclusion. So the variance test fails as one scenario should "HELP" and the other should "HURT".
That's why option A is incorrect.

VeritasKarishma GMATNinja generis Can we explain in this way ?

I misinterpreted this by not realising that "the number acquiring" is not exactly the same as the existing infected -completely different scope change.