In a certain wildlife park, park rangers are able to track the movemen

Male rhinoceroses are also responsiblr for the fertility. If male rhinoceroses did not loose their collars any more often than the female, the immobilization cannot make the fertility lower. Right?

D should be the best

This is a relevant information question. The correct answer will be something where, if it goes one way it will strengthen the argument. If it goes the other way, it will weaken the argument. We can call this the "hybrid strengthen/weaken test".

The argument is: Because females who are frequently recollared have lower fertility rates than females who are not, there is a substance in the tranquilizer dart (the tranq. dart is used in the process of recollaring) that is (probably) causing the infertility.

Let's apply the test to choice C:



If they use the darts VERY frequently for a whole bunch of other reasons, then females who are recollared frequently may have, more or less, equal exposure to the dart relative to all the other rhinos. In that case, the connection between the dart and infertility is weakened--the argument is weakened.

Conversely, if they don't use the dart for any reason other than to recollar, then the link between the dart and infertility is strengthened--the argument is strengthened.

Let's briefly consider the other choices:

Choice A is irrelevant--we don't care about the numbers of collared versus uncollared females. The point is that of those collared infertility incidence is greater. This choice invites you to conflate numbers with percents.
Choice B--"other large mammals"--clearly outside the scope.
Choice D--irrelevant--nothing about the dart.
Choice E--this has nothing to do with the argument.

In assumption question, the assumption should directly hit the conclusion , which states that the tranquilizers causes infertility.

We never know that if the un collared female rhinos are getting the tranquilizers injections or not(even for for other reasons).

So, (B) is incorrect choice.

In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear radio collars. When, as often happens, a collar slips off, it is put back on. Putting a collar on a rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart. Female rhinoceroses that have been frequently recollared have significant lower fetility rate than uncollared females. Probably, therefore, some subtances in the tranquilizer inhibit fertility.

Inevaluating the argument, it would be most useful to determine which of the following?
a. Whether there are more collared female rhinoceroses than uncollared female rhinoceroses in the park.
b. How the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large mammals.
c. How often park rangers need to use trangquilizer dart to immobilize rhinoceroses for reasons other than attaching radio collars.
d. Whether male rhinoceroses in the wild park lose their collar any more often than the park's female rhinoceroses do
e. Whether radio collar is the only pratical means that park rangers have for tracking the movements of rhinoceroses in the park.

Hello.

I have no doubt about the correct choice because it exploits the flaw in the argument.
But I still have a doubt about choice A.
The author makes a comparison between the fertility rates between 2 groups to support his conclusion. If there are 1000 recollared rhinos and 10 uncollared rhinos, and the fertility rates are 50% and 80% respectively, so we have 500 fertile recollared rhinos and 8 fertile uncollared rhinos.

if the difference between numbers of the two groups are too large-- i.e. 1000 and 10 -- and if we accept the author's assumption that the only purpose to shoot rhinos with T darts is to put collar, does the comparison between the fertile rates support the conclusion?

I must ask the question because before I see the correct answer I did not know the flaw of the argument, and the choice A seems good to me. So, if I know the answer for the question, I can eliminate choice A.

Thank you.

This is a nice question with a good degree of difficulty. The key to these questions (evaluating the argument) is to understand assumptions, which are unstated elements that bridge the gap between premises and conclusions. On this question type, your answer will essentially be a question that asks for clarification about a key assumption. As you mentioned, C does provide a question focused on a key assumption (tranquilizers are only used for recollaring).

Now to your question regarding answer choice A. The reason why A would not be our answer is because the premise of the argument deals with fertility RATES not fertility numbers. The GMAT will often shift between figures and rates in the argument/answer choices to throw you off. The use of rates takes the actual numbers out of the equation (essentially normalizing/standardizing the data). Any answer choices that shift from rates to absolute numbers (or vice versa) will not be correct.

KW

Well, only one of them will address the assumption.

The conclusion states that the tranquilizer inhibits fertility. This conclusion is based on the information that recollared rhinos have to be tranquilized in the process and recollared rhinos have lower fertility rates.

The question wants to you evaluate the argument - or in other words to determine what information you would like to have to assess the validity of the argument. To best evaluate the argument, you want some of the "missing" data related to tranquilizer use, recollaring and fertility. Answer choice C gets at that "missing" data by suggesting that there might be other uses for tranquilizers. If there are other uses, we lose our tight connection between recollaring, tranquilizers and fertility and, as a result, we have less confidence in the conclusion. If there are no other uses, that tight connection remains and our confidence in the conclusion increases.

To use your Causation language, the argument notices correlation between recollaring and fertility and asserts that tranquilizers are the cause of the correlation. Answer choice C suggests that we need to know if there are other uses for tranquilizers before we feel comfortable that they are causing the fertility problems.

KW

I will try to put this in simpler terms:
Conclusion : Tranquilizer --> Inhibits infertility
Premise : 2categories of rhinos (collared and uncollared).
We will use the variance test to anayse
options:
C. How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars
strengthen: Very often tranquilizers are used other than collaring--> uncollared sets of rhinos could also be tranquilized under this condition. So if tranqs were to inhibit fertility then this group of uncollared rhinos should become infertile as well
Weaken: Not as much ---> then the conclusion is not that much affected
Hence C

I think the key to solve this problem successfully is to realize that there are 2 groups of rhinos, one with radio tag and other w/o the tag. If you assume that all rhinos are actually being tagged than you wont get to the correct solution. What I want to say is that once a tag fall off than the same rhino is tranquilized again and again and again... and you will say with certainty that the tranq is the culprit for the fertility only if compared with other rhinos w/o a tagg and never been tranqed and their fertility rate.
I admit I would not had that in mind on test day. I assumed that all rhinos in the park were tranqulized in order to get the tag, the difference is that I made a group one more frequently transited and the other group let say only once, and I was looking for answer in these lines and it took me nowere All answers were irelevant , my best bet was on D even though I knew males are not in the argument. If there was expeclitly stated that tehre are rhinos that dont have tagges at all than I would go for C, but I didnt assume that and got it wrong.
Hope my reasoning helps

hi,

the whole logic of this argument depends on the assumption that tranquilizer darts are also used for reasons other than attaching radio collars.
we need to assume this w/o which choice C fails. But, how should we know that we need to consider this assumption while answering?

No, you don't have to assume that darts are used for other purposes. Option (C) tells you that you have to find out whether they are used for other reasons and if yes, then how often are they used. The answer to question in (C) could be 'Never' or it could be 'every week'. This would tell you whether the data you collected about collared rhinos and uncoloured rhinos is reliable.

My take:
In order to evaluate this argument, it would be useful to pre-think the assumptions.
C: some substances in the tranquilizer inhibit fertility in recollared female rhinoceroses.
One assumption could be: Other (uncollared) female rhinos do not have to face the tranquilizer as often as the collared one. Otherwise, how could we say that tranquilizer is the culprit?
Now we can formulate our evaluate Qn around this assumption: How often other (uncollared) female rhinos are tranquilized?
Note: choice C is just a reword of the Q that we just derived.

POE can also be used but chances of mistake increases a bit.

Binit.

The conclusion is that some substance in the tranquilizer probably inhibits fertility.

We are comparing two groups of female rhinos: those who have been recollared frequently (and thus tranquilized frequently) and those who are uncollared (we don't know how often this group has been tranquilized). We know that the first group has lower fertility rates. If we somehow knew that the second group was rarely tranquilized, this would support the author's conclusion that the tranquilizer probably inhibits fertility. But if the second group is frequently tranquilized for other reasons, then the author's argument falls apart, and there must be another explanation for the difference in fertility rates.

I hope this helps!

Its important to note that the premise is a comparison between uncollared (and presumably un-tranquilised) rhinos and collared rhinoes who are shot.

The conclusion is that those who are shot to recollar them have lower fertility than uncollared.

Well if the rangers shoot ALL rhinos for reasons other than recollaring BUT those uncollared rhinos are shot infrequently, then it may be that the increased frequency is to blame for lower fertility.

Alternatively, if uncollared rhinos are shot as frequently, for example say the uncollared rhinos need medical treatment because they are diseased, then it would weaken the claim that the darts are to blame since the uncollared rhinos are shot as frequently as the collared, so we would expect them to have similar fertility.

Hi Karishma,

During my attempt of the free mock I got the same questions with different options, could you also help provide appropriate reasons to reject options and select the correct option for the below options:

In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear radio collars. When, as often happens, a collar slips off, it is put back on. Putting a collar on a rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart. Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. Probably, therefore, some substance in the tranquilizer inhibits fertility.

Which of the following is an assumption on which the argument depends?

a.The dose of tranquilizer delivered by a tranquilizer dart is large enough to give the rangers putting collars on rhinoceroses a generous margin of safety.

b.The fertility rate of uncollared female rhinoceroses in the park has been increasing in the past few decades.

c.Any stress that female rhinoceroses may suffer as a result of being immobilized and handled has little or no negative effect on their fertility.

d.The male rhinoceroses in the wildlife park do not lose their collars as often as the park’s female rhinoceroses do.

e.The tranquilizer used in immobilizing rhinoceroses is the same as the tranquilizer used in working with other large mammals.

I still have a doubt. Even if we know that the rhinos are tranquilized frequently for other reasons, how can we still conclude that tranquilizers are not the main reason for infertility. In order to conclude that we need to know how much of the 'substance' that inhibits the fertility needs to go inside the rhinos to make them infertile. Also we need to know how often the uncollared and how often the recollared rhinos are tranquilized. For example, what if even for other reason the uncollared rhinos are tranquilized far less often. Will the ans to option C help us know how frequently the 2 groups of rhinos (uncollared and recollared) are tranquilized? If not how can I choose option C to help me evaluate whether tranquilizer is the main reason for infertility?
KarishmaB, @GMATNinja- could you please help me understand this?

In 'Useful to Evaluate' questions, we look for an option in which different answers impact the argument differently.

(C) How often do the park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars?
i.e. How often do the rangers tranquillise all rhinos routinely? (whether they have collars or not)

Answer 1: Very often
Well, it seems all rhinos are tranquillised routinely so tranquilliser cannot be the difference between un-collared and frequently re-collared rhinos. If it is done very often for all, a few more times to re-collar may not be the difference maker.
Perhaps carrying the collar itself makes those rhinos lethargic and decreases their fertility (so collared rhinos would have lower fertility than un-collared ones)? Or perhaps there could be some other reason why un-collared rhinos have much better fertility than frequently re-collared rhinos.
But it doesn't look like the tranquilliser is the problem.

Answer 2: Rarely
Then the tranquilliser could be the one causing fertility issues.

Since two different answers lead to different evaluation of the conclusion, option (C) is useful to evaluate.

If we use the negation method in option B, we get:

The fertility rate of uncollected female rhinos has been constant in the past few decades.

This means that the fertility rate fall in collared rhinos is due to tranquillisers because other females rhinos have constant fertility rates.

The fertility rate of uncollared female rhinos has been decreasing in the past few decades.

This is complicated as it actually strengthens the conclusion. If fertility rates of uncollared female rhinos is decreasing, tranquilliser use is not the issue for its fall.

Do we need to reject option B because of this ambiguity?

Can anyone guide on this issue?