LSAT Explanation PT 19, S2, Q2: A large number of drivers routinely

LSAT Question Stem

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

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The passage states that a large number of drivers routinely violate highway speed limits, which is a significant factor in most accidents. The author then concludes that installing devices in all cars to prevent them from traveling faster than the speed limit would prevent most accidents. The structure of the argument is as follows:

Premise: A large number of drivers routinely violate highway speed limits.

Premise: Driving at speeds that exceed posted limits is a significant factor in most accidents.

Conclusion: Installing devices in all cars that prevent those cars from traveling faster than the speed limit would prevent most accidents.

An "Evaluate" question for this argument could be: "Is there any situation where a driver needs to exceed the speed limit to avoid an accident?"

Now, let's discuss the question type and answer choices. This is a Necessary Assumption question, which asks us to identify an assumption on which the argument depends.

a) A person need not be a trained mechanic to install the device properly.

This answer choice is irrelevant to the argument. The passage does not discuss who would be responsible for installing the devices or whether a trained mechanic is required.

b) Most accidents are caused by inexperienced drivers.

This answer choice is also irrelevant. The argument focuses on the fact that driving at speeds that exceed posted limits is a significant factor in most accidents. It does not mention the experience level of the drivers.

c) A driver seldom needs to exceed the speed limit to avoid an accident when none of the other drivers involved are violating the speed limit. (Correct Answer)

This answer choice is a necessary assumption because it addresses a potential counterargument. If there are situations where a driver needs to exceed the speed limit to avoid an accident, installing devices that prevent them from doing so could potentially lead to more accidents. By assuming that drivers seldom need to exceed the speed limit in such situations, the argument is strengthened.

d) Most drivers who exceed the speed limit do so unintentionally.

This answer choice is irrelevant to the argument. Whether drivers exceed the speed limit intentionally or unintentionally does not impact the conclusion that installing devices to prevent speeding would prevent most accidents.

e) Even if the fines for speed-limit violations were increased, the number of such violations would still not be reduced.

This answer choice is not a necessary assumption because it introduces an alternative method of reducing speed-limit violations (increasing fines). The argument does not claim that installing devices is the only way to prevent accidents, just that it would be an effective way. Whether or not increasing fines would reduce violations does not impact the conclusion that installing devices would prevent most accidents.

In conclusion, the correct answer is C, as it is a necessary assumption for the argument. The other answer choices are either irrelevant or introduce alternative methods that do not impact the conclusion.