In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear...

GMAT Critical Reasoning : (CR) Questions

Source: Official Guide

Critical Reasoning

Assumption

MEDIUM

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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?

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.

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

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

The male rhinoceroses in the wildlife park do net lose their collars as often as the park's female rhinoceroses do.

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

Solution

Passage Analysis:

Text from Passage	Analysis
In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear radio collars.	What it says: Park rangers track rhinos using radio collars What it does: Sets up the basic situation and explains why collars are used What it is: Background information Visualization: Wildlife Park: 25 rhinos total, 20 wearing radio collars being tracked by rangers
When, as often happens, a collar slips off, it is put back on.	What it says: Collars frequently fall off and need to be replaced What it does: Shows this is a recurring problem that builds on the collar system What it is: Additional context
Putting a collar on a rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart.	What it says: Recollaring requires tranquilizing the rhino What it does: Reveals the process behind replacing collars, connecting to the previous statement What it is: Procedural information
Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females.	What it says: Frequently recollared females have much lower fertility than uncollared females What it does: Introduces key evidence about fertility differences, building on the recollaring process What it is: Observational data Visualization: Fertility Comparison: Frequently recollared females: 40% fertility rate, Uncollared females: 85% fertility rate
Probably, therefore, some substance in the tranquilizer inhibits fertility.	What it says: The tranquilizer likely contains something that reduces fertility What it does: Draws a conclusion from the fertility evidence presented What it is: Author's conclusion

Argument Flow:

We start with background about how rhinos are tracked with collars, then learn that collars often slip off and need replacement using tranquilizers. The key evidence shows frequently recollared females have lower fertility than uncollared ones. From this, the author concludes the tranquilizer must contain fertility-inhibiting substances.

Main Conclusion:

Some substance in the tranquilizer dart inhibits fertility in female rhinoceroses.

Logical Structure:

The argument uses a correlation between frequent tranquilizer exposure (through recollaring) and lower fertility to conclude that the tranquilizer causes the fertility problems. The evidence directly links repeated tranquilizer use to reduced fertility, leading to the causal conclusion.

Prethinking:

Question type:

Assumption - we need to find what the argument must assume to be true for the conclusion to hold. The conclusion is that some substance in the tranquilizer inhibits fertility.

Precision of Claims

The argument makes specific claims about frequency (frequently recollared vs uncollared), fertility rates (significantly lower), and causation (tranquilizer substance causes fertility inhibition).

Strategy

To find assumptions, we need to identify ways the conclusion could be false while keeping all the passage facts true. The author concludes that tranquilizer substance causes lower fertility, but there could be other explanations for why frequently recollared females have lower fertility rates. We need to find what the argument must assume to rule out alternative explanations.

Answer Choices Explained

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.

This choice discusses the safety margin for rangers administering tranquilizers. The argument's conclusion about tranquilizer substances inhibiting fertility doesn't depend on how safe the dose is for the rangers. Whether the dose provides a generous safety margin or not has no bearing on whether substances in the tranquilizer affect rhino fertility. This is completely irrelevant to the causal relationship the argument is trying to establish.

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

This choice mentions whether uncollared female fertility rates have been increasing over decades. The argument compares frequently recollared females to uncollared females at the same time period. Whether uncollared fertility has been trending upward over decades doesn't affect the validity of comparing these two groups' current fertility rates. The conclusion about tranquilizer effects doesn't require any assumption about historical fertility trends.

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

This choice states that stress from immobilization and handling has little or no negative effect on fertility. This is exactly what the argument must assume. If stress from being tranquilized and handled significantly reduced fertility, then the lower fertility in frequently recollared females could be explained by repeated stress rather than by tranquilizer substances. The argument depends on ruling out stress as an alternative explanation to establish that tranquilizer substances are the cause. Without this assumption, the conclusion falls apart.

The male rhinoceroses in the wildlife park do net lose their collars as often as the park's female rhinoceroses do.

This choice compares how often male versus female rhinos lose their collars. The argument only deals with female fertility rates and doesn't make any claims about or comparisons to males. Whether males lose collars more or less frequently than females has no impact on the conclusion about tranquilizer substances affecting female fertility. This is outside the scope of the argument.

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

This choice discusses whether the same tranquilizer is used for other large mammals. The argument's conclusion about this specific tranquilizer inhibiting rhino fertility doesn't depend on what tranquilizers are used for other species. Whether it's the same or different tranquilizer used elsewhere doesn't affect the causal relationship between this tranquilizer and rhino fertility that the argument is establishing.

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