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.
This question really made me bewildered as to what kind of logical reasoning is in GMAT. Please help.
OA is C

I am not able to justify the OA. Could somebody help ?

the best way to "justify" the oa here is to eliminate the other answers. this is more straightforward than on many other problems, because ALL of the wrong answers are VERY much outside the argument's scope.

(a) irrelevant, as the numbers of collared vs. uncollared rhinos are irrelevant to fertility rates (presumably measured in babies per rhino, or # of copulations required per pregnancy, or some other figure that doesn't have anything to do with the total population size).

(b) irrelevant; the argument deals only with rhinos.

(d) irrelevant; the argument deals only with FEMALE rhinos.

(e) irrelevant; the purpose of the collar doesn't affect the fertility issue. moreover, other means of tracking the rhinos lie outside the scope of the argument.

--

that leaves (c).

the reason (c) matters is because the study purports to cover the differences between rhinos that have been hit with tranquilizer darts (let's call them "tranks") and those that haven't. however, the study DOESN'T directly split the rhinos into "trank" and "non-trank" groups; it splits them into "frequently recollared" and "not frequently recollared" groups.
the argument therefore depends on the assumption that "frequently recollared" is an adequate proxy for "been hit by tranks" and that "not frequently recollared" is an adequate proxy for "not been hit by tranks".
choice (c) is very much relevant to this assumption, because that association falls apart if the rhinos are getting tranked for lots of other reasons in addition to the collar issue.

but again, the wrong answers are easy pickings here, so you probably don't even need to think this much.

--

the real question is whether the rhinos can pop their collars.
;)

This is a causal assumption critical reasoning question so I’m looking to evaluate (the conclusion) whether some substances in the tranquilizer inhibit fertility (and not frequent ‘recollaring’ of female rhinos)

I believe the conclusion of the stem is "Probably, therefore, some substances in the tranquilizer inhibit fertility." So the author is not attributing the lowering of fertility to the frequent ‘recollaring’ but rather to some substances in the tranquilizer. I believe that choice "C" doesn’t help in evaluating the argument whether some substances in the tranquilizer inhibit fertility. What would help evaluating the argument is a question about a possible different cause (other than tranquilizers) for decrease in fertility.

I’m sure my reasoning is wrong because GMAT Prep and Manhattan Gmat can’t be wrong. So why is the reasoning I have mentioned above incorrect? Could you please elucidate this and the reasons why C is correct?

did you read the post directly above yours?

if not, read it.

if you did, then please explain what you didn't understand, since that post explains the logic of this problem.

the argument isn't suspect because of anything directly involving its conclusion; that would be too easy. instead, it's suspect because it equates "been hit with tranquilizers" with "frequently re-collared". if those two things aren't actually equivalent, then the whole argument is invalid.

remember, if any link, anywhere in an argument, is invalidated, then the whole argument is invalidated. you don't have to attack the actual conclusion of the argument.

Ron,

Thanks a lot for wonderful explanation.

I always thought that in "evaluating the argument" questions, we need to consider whether the argument follows from the premises, and then attack the conclusion to find out whether argument is weak or strong, sound or unsound.

But its nice to know a new concept that in such questions, we need not always attack the conclusion.

As this is a new concept for me , I request you to throw some more light on this concept using 2-3 similar questions.

Thanks in advance !!

hi -

an argument is a unified, organic whole. if you invalidate any logical step of the argument, then you invalidate the conclusion.

this is much like attacking a chain that's securing a chandelier to a ceiling.
attacking the conclusion itself is like attacking the link of the chain that's actually attached to the chandelier.
attacking a logical connection between other premises is like attacking one of the links in the middle of the chain.

both of these will invalidate the argument, just as both of the analogous physical acts will cause the chandelier to fall.

--

as for "2-3 different questions", perhaps you could post those yourself, and we could analyze them?
thanks.

Hi Ron

This question is surprising to me.
I understand that there is a flaw in the statement-Female rhinoceroses that have been frequently recollared have significant lower fetility rate than uncollared females-and i have read your post above.
But even the flaw does not help dispute the conclusion- Probably, therefore, some subtances in the tranquilizer inhibit fertility-in that even if rhinos have been tranquillized lot of times other than re-collaring, the assertion that some subtances in the tranquilizer inhibit fertility remains intact and sound.

I also read your statement-if you invalidate any logical step of the argument, then you invalidate the conclusion.-but i have not seen any GMATPrep question in which the correct answer bolster the flaw in evidence/premise but, if taken together with conclusion, does not affect the conclusion.
Can you show me some examples of this sort?

Thanks

no.

in the FACTS in the passage, fertility is ONLY connected to re-collaring. NONE of the facts connect fertility DIRECTLY to the tranquilizer dart IN ANY WAY AT ALL.

therefore, in order to relate fertility to the tranquilizer darts, you must assume that there is a necessary connection between re-collaring and the tranquilizer dart.

if you break the connection between tranquilizers and collaring, then collars have NO connection left to fertility AT ALL.

hope that helps.

An assumption of this argument is that the number of times a female rhino has her collar reattached is a good proxy for the umber of times she is tranqed. C speaks to whether that assumption is true.

If a state of affairs would be "useful to determine" in evaluating a argument, then different versions of that state of affairs should give different verdicts on the soundness of the argument.

Consider two different outcomes you might come across if you determined C. First, maybe female rhinoceroses are never tranqed except to have collars reattached. This would weigh in favor of the argument that tranqing them inhibits their fertility, since it would suggest that the number of times a female rhino has had its collar reattached is a good indication of the number of times she has been tranqed. Second, maybe female rhinoceroses are tranqed all the time. This would weigh against the argument since it would suggest that the number of times a female rhino has had its collar reattached is a poor indication of the number of times she has been tranqed.

If the thing that corresponds to infertility--having a collar reattached--doesn't correspond particularly well to getting tranqed, then there's little reason to suppose that infertility corresponds to getting tranqed.

Yes, I realize that I just wrote the same thing four different ways, and that Ron had already contributed pretty much the same substance. Is it getting any clearer?

@mschwrtz,
your explanations with that of Ron have done a great deal of clarifications to my dumb brain- had to go through the posts several times.

Your explanation has it that, for example;

(i)TRANCKED = 100
RECOLLARED = 4
TRANCKED (BUT NOT RE-COLLARED) FOR SOME OTHER REASONS:96

(ii)TRANCKED = 100
RECOLLARED = 96
TRANCKED (BUT NOT RE-COLLARED)FOR SOME OTHER REASONS:4

Option C sought to distinguish between (i) and (ii) as the former clearly shows that "TRANCKING" has little or no direct relationship with infertility. Since the argument suggests that rate of infertility = rate of trancking, option C exposes the error in the line of thought.

Mschwrtz, hope am correct anyway?

looks like you have a good understanding of this one, joe..

_________________
Tim Sanders
Manhattan GMAT Instructor

The key part of the question is that the author is comparing frequently recollared Female rhinoceroses with uncollared females, and he concluded that the tranquilizer is the cause of low fertility.

So:
frequently recollared Female --> frequently exposed to tranquilizer --> low fertility rate (as compared to uncollared female)

If C is true: the rhinoceroses would also be immobilized for other purpose, e.g. for the purpose of body check-up:

Frequent check-up (for uncollared) --> also expose to tranquilizer --> fertility rate is not affected

CONCLUSION: the tranquilizer is not the cause of low fertility.

==> C is correct.