Logical Reasoning

PT113 · S4 · Q17 A year ago the government

A free, expert breakdown of this official LSAT Logical Reasoning question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

A year ago the government reduced the highway speed limit, and in the year since, there have been significantly fewer highway fatalities than there were in the previous year.

Conclusion

Speed limit reduction can reduce traffic fatalities.

Evidence

Since we lowered the speed limit a year ago, there have been way fewer highway fatalities than in the previous year.

Evaluate

There is a Curious Comparison -- why are this year's traffic fatalities so much lower than last year's?

The author assumes a Causal Explanation for it -- the new speed limit caused the reduction in fatalities.

What are the two lenses through which we evaluate every Curious Fact / Explanation argument? - is there some Other Way to explain the curious fact? - how plausible is the Author's Way?

How else could one explain a reduction in traffic fatalities? - fewer drivers - better road conditions - more policing, which deters aggressive driving etc.

How would we assess the plausibility of the author's hypothesis? - in nearby areas where the speed limit didn't change, were the fatalities still as high as last year? - are people obeying the new speed limit? i.e., has average driving speed actually decreased?

Goal

Since this is Necessary Assumption, we would primarily look to rule out an Alternate Explanation for why fatalities are lower this year, but we'd also consider an answer that states something required for the author's story to be plausible (such as ).

17.

The argument is most vulnerable to the criticism that it takes for granted that

  1. highway traffic has not increased

    Opposite

    When we see a Necessary Assumption answer choice ruling out a possibility with "not", we get very intrigued. We want to negate it and see if it weakens the argument. Would this negation hurt the argument? Highway traffic has increased over the past year. No that would strengthen the argument. If we have fewer fatalities even though there's more highway traffic, it sounds like something has really helped cut down on fatalities in the past year! (hint-hint: new speed limit) We could also say that this negation would strengthen the argument because it rules out the possibility that fatalities are lower this year because highway traffic is lower. This answer would be correct if it said, "highway traffic has not significantly decreased over the past year"

    4% picked this

  2. the majority of drivers obeyed

    Too Strong: most / obeyed

    In 99% of cases, the word/concept of "most" will be wrong on Necessary Assumption. When you negate that idea, you go from 51% to 49%. Does it badly weaken this argument if 49%, rather than 51%, of drivers obeyed the new speed limit? Of course not. The author's explanation definitely assumes that "a significant number of drivers have changed their driving speed in reaction to the new speed limit", because if almost no one changed their driving in reaction to the new speed limit, then we couldn't say that the new speed limit explains the drop in highway fatalities. But this answer is formulated way too strongly and specifically.

    20% picked this

  3. there is a relation between

    Out of Scope: number of accidents

    Very close, but the author is assuming there's a relationship between speed limit and the rate of highway fatalities. If we say there's no relation between speed and number of accidents, we're saying, "People drive like jerks and there's gonna be ~10,000 accidents a year no matter what". But that doesn't badly weaken the author's argument. She can still believe that by lowering the speed limit and thus (she assumes) lowering the average driving speed of cars, that same number of accidents could result in significantly fewer fatalities.

    23% picked this

  4. the new speed limit was

    Unnecessary Comparison: more strictly

    The author does not need the new one to be more strictly enforced than the old one. If the old one was strictly enforced, then the new speed limit could be just as strictly enforced and the argument would be fine. The author is assuming that the new posted speed limit is the causal difference-maker. She's not assuming that an increase in police presence is the causal difference-maker.

    8% picked this

  5. Correct

    the number of traffic fatalities

    Why this is right

    When we see a Necessary Assumption answer choice ruling out a possibility with "not", we get very intrigued. We want to negate it and see if it weakens the argument. Would this negation hurt the argument? the number of fatalities the previous year was abnormally high Yes, that provides the alternate explanation we were suspecting. This is just an alternate explanation that people don't see much: regression to the mean ... a return to normalcy. Consider this analogy: Our flower shop's revenue was down 45% this month compared to last. At the beginning of this month, we changed the sign on our window, so apparently new signage on your storefront can reduce store revenue. If we objected, "Yo ... this month is March. Last month was February, aka Valentine's Month, aka a month of abnormally high revenue for a flower shop. Obviously March is going to be 45% lower than February. That's because March is a normal month, and the previous month was just an outlier. We don't need to blame this on the new sign. We can just attribute this to a return to our normal baseline revenue." This answer rules out an alternate explanation for the curious fact. Fatalities aren't necessarily down this year because we did something new. we would have expected them to be down even if we had done nothing new, since last month was the outlier / the aberration / the funky thing that needs to be explained. Normalcy doesn't need an explanation. Deviations from normalcy do.

    Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.

    44% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free