In a national park located on an island, a herd of moose was

Question

In a national park located on an island, a herd of moose was increasing in number and threatening to destroy species of native plants. Wolves were introduced to the island to reduce the herd and thereby prevent destruction of the vegetation. Although the wolves prospered, the moose herd continued to grow.

Which one of following, if true, most helps to explain the failure of the strategy involving wolves?

(A) The presence of wolves in an area tend to discourage other predators from moving into the area

(B) Attempts to control moose populations in other national parks by introducing predators have also been unsuccessful

(C) Wolves often kill moose weakened by disease that probably would have spread to other moose

(D) Healthy moose generally consume more vegetation than do those that are diseased of injured

(E) Moose that are too old to breed are just as likely to die of natural causes as of attack by wolves

ridhiagarwal · Answer

can someone please explain why the answer is not A?

vmkumar · Answer

Here the concentration is only on wolves, but not on other predators. We don't know whether other predators prey on the moose.

Posted from my mobile device

GMATin · Answer

Hi  ridhiagarwal ,

Happy to help!

A tells us that because of wolves other predators might not be able to enter the park. If we consider this to be true, we are still left with two outcomes: 1) either the wolves are enough to control the moose population or 2) the wolves are not enough to control the population. Since this option can reach either of the outcomes, we cannot mark this as the right answer.

On the contrary, let us understand why C is the correct answer.

If we consider C to be true, then we are told that out of the various ways in which the moose population could reduce (predator attack, disease, etc), one of the ways is largely eliminated by the wolves. So, there is essentially a part of the moose population which is not dying because the wolves have reduced the possibility of death by disease. Hence, the only outcome of this situation is that the population is rising instead of reducing.

Hope this helps!

abhishekmayank · Answer

Very reluctant to accept option C as the right answer :

(C) Wolves often kill moose weakened by disease that probably would have spread to other moose

1. How can we conclude that a disease infected moose is bound to die, and hence effectively helps decrease the overall 
 moose population ?
2. Whether "probably" can lead to a definite conclusion ?

AnirudhaS · Answer

If you were down to A and C, thats good enough and move on. I personally feel that this question is not air-tight.

Axelkr00 · Answer

I agree with all of your points. This answer isn't airtight. But generally, in GMAT CR we don't have to prove something is absolutely true. Rather we have to choose the best option out of the 5. Sometimes the answer will be ideal but sometimes it'll just be the best answer out of the 5.

Here we don't have an ideal answer. A and C are the 2 best answers. Between the two, choice C definitely helps resolve the paradox better than A does.

abbyrox_247 · Answer

Why is the answer not E? It would mean the wolves are killing old moose who were going to die anyway, plus they can't breed, hence the rise in their population

Axelkr00 · Answer

Hey abbyrox_247,

In general on CR, you should be very careful about what you can infer from the stimulus and the answer choices. You seem to have gone too far with answer choice E. All it says is that the probability of an old moose dying from natural causes is equal to the probability of an old moose dying from a wolf attack. Does this mean that wolves are killing old moose? No it doesn't.

Let's say that today I'm just as likely to eat pizza as I am to eat a burger. Can you conclude that I ate a burger today just because the two probabilities are equal? Nope, this would be flawed reasoning.

There are plenty of other problems with E too. For starters we don't even know if there are any old moose in this national park. For all we know, perhaps all the moose are young, therefore making this answer choice irrelevant since it only talks about old moose. Secondly, it is reasonable to assume that the authorities that introduced the wolves are mostly interested in moose that can breed and hence can increase the population. They would probably know that killing moose that are too old to breed won't solve their problem. Lastly, even if we assume, as you said, that wolves are killing old moose only, it still does not help resolve the paradox. E talks about a subset of the population and we are concerned with the entire population. Why didn't the wolves attack the other moose? This answer choice doesn't address that.

As you can see there are plenty of problems with E, all of which indicate that this choice is irrelevant and doesn't resolve the discrepancy.

Its_me_aka_ak · Answer

Your reasoning to elaminate E seems to be problematic 
1.Probability of a old moose being killed by wolf is 50-50 
But probability of moose being killed by a disease is unknown 
So E>B
2. Yes we dont know if there are any old moose or old moose that have not died already naturally or by wolves (probability of finding an old moose is unknown)
Similiarly, we do not know if there is any moose affected by any disease or have not died already (probability of finding a moose affected by any disease is unknown too)
So E=C + we donno if wolves are killing either of them

3. If wolves are only killing old moose they pretty much became full if they ate them, or they were tired of killing them as we donno if moose can fight back or nah. On the other hand, diseased goose are easier to kill as suggested by the passages. Also not to mention, if diseases can kill them or not is still unknown 
E slightly but > C

Posted from my mobile device

Axelkr00 · Answer

Your inferences seem to be going in the wrong direction too.

Nowhere is it stated that the  probability  of the two events is  split evenly  between them and is therefore 50-50. All we know is that the two events have an  equal  chance of occurring. It could be 30-30, with other causes of death comprising the remaining 40%. Secondly, answer choice C has little to do with moose and more to do with wolves. It says wolves often kill infected moose. Often means 70-80% of the time. Let's explore two cases : a) There are some moose which are infected. b) There are no infected moose.

Case a) The wolves mostly killed infected moose and few healthy moose. In this case, we can expect a rise in the population since the healthy moose are still reproducing. The infected moose that died would have weakened the healthy moose if they weren't killed because C says that their disease would have probably spread to other healthy moose and hence a chain of infections would have weakened a large portion of the total. But because the wolves eliminated this disease from spreading and since the wolves mostly kill weakened moose, the population flourished and therefore the paradox is solved.

Case b) Every single moose is healthy and there are no infected moose. Since the wolves often kill infected and weak moose, they'll have little impact on healthy ones. Consequently, because there are no infected moose and because the wolves aren't effective predators of healthy moose, the moose population flourishes and the paradox is solved.

Nevertheless, if you're still not convinced, you can go on any LSAT forum and look up this question. You'll find that the official answer provided by LSAT itself is C and in the explanations you'll come across similar reasons for elimination. I agree that this answer isn't perfect or airtight. But, as is often the case, we aren't allowed to advocate our own ideal and perfect versions of answering the question. We just have to pick the best of the 5 given or, in some cases, the least worst of the 5. In this CR question, C helps resolve the discrepancy more than the others.

abbyrox_247 · Answer

Thanks Axelkr00, I get your point now and it makes sense, if E said 'Wolves often kill old Moose..' it would be a strong contender.

Its_me_aka_ak · Answer

Your inferences seem to be going in the wrong direction too.

Nowhere is it stated that the  probability  of the two events is  split evenly  between them and is therefore 50-50. All we know is that the two events have an  equal  chance of occurring. It could be 30-30, with other causes of death comprising the remaining 40%. Secondly, answer choice C has little to do with moose and more to do with wolves. It says wolves often kill infected moose. Often means 70-80% of the time. Let's explore two cases : a) There are some moose which are infected. b) There are no infected moose.

Case a) The wolves mostly killed infected moose and few healthy moose. In this case, we can expect a rise in the population since the healthy moose are still reproducing. The infected moose that died would have weakened the healthy moose if they weren't killed because C says that their disease would have probably spread to other healthy moose and hence a chain of infections would have weakened a large portion of the total. But because the wolves eliminated this disease from spreading and since the wolves mostly kill weakened moose, the population flourished and therefore the paradox is solved.

Case b) Every single moose is healthy and there are no infected moose. Since the wolves often kill infected and weak moose, they'll have little impact on healthy ones. Consequently, because there are no infected moose and because the wolves aren't effective predators of healthy moose, the moose population flourishes and the paradox is solved.

Nevertheless, if you're still not convinced, you can go on any LSAT forum and look up this question. You'll find that the official answer provided by LSAT itself is C and in the explanations you'll come across similar reasons for elimination. I agree that this answer isn't perfect or airtight. But, as is often the case, we aren't allowed to advocate our own ideal and perfect versions of answering the question. We just have to pick the best of the 5 given or, in some cases, the least worst of the 5. In this CR question, C helps resolve the discrepancy more than the others.

Thanks for sharing your reasoning bro. my main reason to cut C was that the infection may be contagious but there is no proof if infected moose will die or at least stop reproducing and on the other hand option E actually explains that wolves kill moose that were dying anyway so that provides us a reason why wolves failed to stop the herd from growing.

SwethaReddyL · Answer

GMATNinja  /  KarishmaB  - could you please explain your thoughts on this particular cr? Why is option A wrong here?

guddo · Answer

In a national park located on an island, a herd of moose was increasing in number and threatening to destroy species of native plants. Wolves were introduced to the island to reduce the herd and thereby prevent destruction of the vegetation. Although the wolves prospered, the moose herd continued to grow. 
 
Which one of following, if true, most helps to explain the failure of the strategy involving wolves?

The plan assumed that introducing wolves would reduce the moose population. But if wolves mainly kill moose that would otherwise spread disease, then wolves may actually help the overall herd stay healthier and keep growing.  That explains why the strategy failed .

(A) The presence of wolves in an area tend to discourage other predators from moving into the area

This does not help much. The island already had wolves introduced, but we are not told other predators would have reduced the moose population.
(B) Attempts to control moose populations in other national parks by introducing predators have also been unsuccessful

This says similar strategies failed elsewhere, but it does not explain why this one failed.

(C) Wolves often kill moose weakened by disease that probably would have spread to other moose

This is correct. If wolves kill diseased moose before those moose spread disease, then wolves may reduce disease transmission within the herd. So the herd can continue growing despite wolf predation.

(D) Healthy moose generally consume more vegetation than do those that are diseased of injured

This explains why healthy moose may damage vegetation more, but it does not explain why the moose herd continued to grow.

(E) Moose that are too old to breed are just as likely to die of natural causes as of attack by wolves

This does not explain the continued growth of the herd. Killing nonbreeding old moose would not strongly reduce future population growth, but the option does not show that wolves mainly killed such moose.

Answer: (C)

egmat · Answer

Hi SwethaReddyL,

Good question, because (A) is the classic "sounds relevant, but watch the gap" trap here.

The paradox we need to explain: the wolves  prospered  (so they were eating), yet the moose herd  kept growing  anyway. Whatever we pick has to account for that.

Now look at the exact words of (A):  "The presence of wolves... tends to discourage other predators from moving into the area."

For (A) to explain the failure, you have to assume something the stimulus never tells you - that  those other predators would have preyed on the moose , so keeping them out cost the moose some deaths. But the argument says nothing about other predators eating moose. As vmkumar pointed out earlier in the thread,  "we don't know whether other predators prey on the moose."  Strip that assumption away and (A) does nothing to the puzzle. That's the precise flaw:  true-but-irrelevant - it only works if you smuggle in an outside fact.

Contrast that with (C): the wolves kill  diseased  moose whose disease  "probably would have spread to other moose."  So the wolves removed the very animals that would have wiped out a chunk of the herd - keeping the rest healthy and breeding. That directly explains why the herd grew even as the wolves thrived. No outside assumption needed.

Watch one word turn

See how easily (A) becomes a real contender if we just add the missing link:

- As written:  "discourage other predators"  - silent on whether they hunt moose, so it explains nothing.
- If it said:  "discourage other predators  that were the moose's main hunters "  - now it would explain the growth, and it'd compete with (C).

The takeaway: judge (A) only on what it actually states, not on the helpful backstory your mind fills in. The moment a choice needs you to supply a fact the stimulus didn't give, it's out.

Answer: C

In a national park located on an island, a herd of moose was

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GMAT Critical Reasoning (CR) Questions

In a national park located on an island, a herd of moose was

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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Perfect 805 Score Debrief by Julia

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