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#35308
Complete Question Explanation

Strengthen—PR. The correct answer choice is (E)

This stimulus consists of two premises and a conclusion. The first premise is that the government
study shows that raising the speed limit to actual average speeds on level, straight, high-speed
roadways reduces the accident rate. Next, we are told that the average speed for such roads is 75
miles per hour (120 kph) and the author thus concludes that all such roads should have that speed
limit. Note that the scope in all three sentences is identical and consistent (i.e, “level, straight
stretches of high-speed roadways”). Since the scope is appropriate, the author could justifiably
conclude that raising the speed limit to 75 mph on these roadways would reduce the accident
rate. Instead, the author concludes that the speed limit should be raised. While this may seem an
insignificant leap in logic, the author’s shift from a predicted outcome to a recommended approach is
unsupported without first establishing the desirability of the outcome. The correct answer will be a
principle that supports this leap.

Answer choice (A): The author’s argument is not strengthened by demonstrating that such changes
should not be made on any other kind of road. The consistent scope of both premises and the
conclusion eliminates the need to deal with other kinds of roads and renders this principle irrelevant.

Answer choice (B): By the same token as (A), the consistent scope throughout our stimulus frees
us from the need to consider other roads. Furthermore, suggesting that the speed limit on all roads
should be raised to 75 mph mistakenly generalizes the findings of the government study, which was
specific to level, straight stretches of high-speed roadways.

Answer choice (C): Our premises indicate that the speed limit for these types of roads “tends to be”
75 mph. If “tends to be” is interpreted as “all such roadways have roughly equal average speeds”,
then we have satisfied a necessary condition of this principle, which would allow but not justify our
reasoning. If this principle is understood to imply a higher standard than our premise has met, then
(C) would weaken the reasoning above. In neither case does this principle help to justify the author’s
conclusion.

Answer choice (D): (D) raises a number of questions. Are current speed limit laws long-standing?
Does an average speed of 75 mph indicate that laws are “widely violated” or could a few extremely
fast cars account for the average speed? If speed limit laws are long-standing and widely violated,
does classifying them as “probably bad laws” justify the conclusion? What does this principle have
to do with the rationale of reducing accidents? There are far too many issues with (D) to use it as
justification of the reasoning in the stimulus.

Answer choice (E): This is the correct answer choice. The government study gives us a
measure that reduces the rate of traffic accidents. The author concludes that this measure should
be implemented. The best way to justify this reasoning is apply a principle that “any measure that
reduces the rate of traffic accidents should be implemented.” Such a principle effectively bridges the
gap between the expected outcome of the measure and the desirability of implementing it.
 allisonellen7
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#17366
Hi there! I am confused why B couldn't be the correct answer. Couldn't it justify why the conclusion says that 75 miles per hour should be set as a uniform national speed limit, instead of that each region/state/locality should set the speed limit to their average speed of traffic on level, straight stretches of high-speed roadway? Thank you!
 Emily Haney-Caron
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#17373
Hi Allison Ellen,

Even if B were true, that doesn't explain anything about why the speed should be increased to 75; instead, as long as it was uniform, we could set a uniform speed limit of 15 mph and the principle in B would still be followed. E is the only answer that justifies the particular speed limit in the conclusion.
 Rita
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#29580
Hi Emily,

Why is justifying the particular speed limit more important than justifying the areas to which it applies? The conclusion introduced a new idea (uniform national speed limit) in the conclusion, so that was the aspect I tried to justify (choosing B). I kept E as a contender, but I'm still not clear on why it's a better choice than B.

Thanks,
Rita
 Claire Horan
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#29623
The first sentence establishes that raising the speed limit to the actual average speed on these types of roadways reduces the accident rate. The second sentence says that the speed limit on these roads should therefore be set to that average speed. The first sentence is descriptive. The second sentence is prescriptive, arguing what "should" be done. As Emily explained, answer choice (B) doesn't justify why the speed limit should be 75. Answer choice (E) justifies the speed limit of 75 (because it reduces the rate of traffic accidents). The uniformity is a by-product of the study finding that the average speeds on these types of roads "tends to be" 75. If the study had not found that "level, straight stretches of high-speed roadways" had the same average speed, the reasoning would not be justified. In other words, the evidence from the study was what led to the conclusion, not an outside principle. "Justify the reasoning" questions will require a principle that is missing from the stimulus. In that way, they are similar to assumption questions.
 siennahwoo
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#33567
How is this questions type different from the "justify the conclusion" question type?
 Robert Carroll
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#33569
Sienna,

This is a Strengthen because the question qualifies the degree of proof needed: it says "most helps to justify," leaving open the possibility that the answer will help, but not 100% prove the conclusion.

Robert Carroll
 bk1111
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#39128
Can someone elaborate on why C is incorrect? I don't fully understand the reasoning above. Additionally, I eliminated E because I thought the scope of "any measure that reduces traffic" was too big, since the stimulus is referring specifically to raising speed limits.
 Adam Tyson
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#39505
Think of it mathematically, bk1111: the author says that raising speed limits to match the average for this particular type of road reduces accidents. He then concludes that we should do that. How do you strengthen the claim that we should do that? By saying that you should do things that reduce accidents. It may seem very obvious when put that way, but that's often what we are looking for - an obvious link to close a gap between the premises and the conclusion.

Answer C doesn't help the conclusion that we should do it, because it only says that we should do it ONLY if the roads all have the same average speed of traffic. Do they? We don't know - we only know what the overall national average is, without differentiating between different roadways of that type. Even if we did know that all those roadways had the same average speed as each other, saying that those are the ONLY circumstances under which we should institute the new rule doesn't strengthen the claim that we should actually institute that rule. That would be like saying you should only go scuba diving if you have a full oxygen tank, and concluding that anyone with a full oxygen tank should go scuba diving. Maybe some people with full tanks are just learning, and they shouldn't go do it yet?

I hope that clarifies it for you!
 cmorris32
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#78248
This question felt exactly like the June 1997 Section 4 #13 car phone question!!! As I was completing this question I was thinking to myself that I have seen a very similar question before. Definitely helped me answer this question!!!

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