Logical reasoning PrepTest 142 · Section 2 · Question 21

Incorrect. There's no indication that the high-speed roadways are the only roads the speed limit should apply to. This answer also ignores the qualifier—level, straight stretches of these roads.

Incorrect. This answer justifies implementing a standard speed limit on all high-speed roadways, but not necessarily the higher one reflecting actual speeds driven as the argument concludes.

Incorrect. This answer establishes a necessary condition for implementing a uniform national speed limit, not a sufficient one, so it doesn't justify a conclusion that such a speed limit should be implemented. Remember, principles/conditionals are used in argument by establishing the sufficient condition as a premise and concluding the necessary condition, so Principle (Strengthen) questions need the necessary condition of the principle to line up with the conclusion in the stimulus.

Incorrect. This principle might justify a conclusion that a law isn't a good law, but it doesn't justify a conclusion that a certain law should be changed/implemented.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Principle (Strengthen)

Stimulus Summary:
Study—Raising the speed limit on level, straight highways to what people actually drive lowers accidents.
Fact—On these highways, the average speed is 75mph (get out of here, metric system!)
Conclusion—Level, straight highways should have their speed limit set to 75mph

Answer Anticipation:
Principle (Strengthen) questions connect the reasoning in the premises to the judgment in the conclusion. Here, the conclusion is that the government should increase the speed limit on certain roads to 75mph (the speed people actually drive). Why? Because studies show it'll lower the accident rate.

So the correct answer should connect lowering the accident rate to changing traffic laws/the speed limit:

If a change to traffic laws/speed limit would save lives, then the government should make that change.

Answer Explanation:
Studies show that raising the speed limit on level, straight stretches to 75mph will lower accident rates. If, as this answer states, anything that reduces accidents should be implemented, then this change to the speed limit should be implemented—as the conclusion states.

Key Takeaway:
Principles/conditionals are used by argument to establish rules that are then applied to specific situations. To apply a principle/conditional, the sufficient condition needs to be established in a premise in order to conclude the necessary condition. As such, only necessary conditions can be concluded.