Logical Reasoning

PT151 · S3 · Q21 In an experiment, some volunteers

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

In an experiment, some volunteers were assigned to take aerobics classes and others to take weight-training classes.

Conclusion

Aerobic exercise helps the body handle psychological stress.

Evidence

In an experiment, the volunteers who were assigned to take aerobics classes had lower measurable stress symptoms following a tough math problem than did the volunteers who were assigned to take a weight-training class.

Evaluate

The verb "helps" in the conclusion is Causal. Since the author is making a causal interpretation of a study, we can use our Curious Fact / Explanation mindset.

Curious Fact Why did the people who were assigned aerobics have less stress after the hard math problem than did the people who were assigned weight-training?

Author's Explanation Aerobics helps the body handle psychological stress.

We can affect these types of arguments in two ways: - considering Alternate Explanations for the Curious Fact - assessing the plausibility of the Author's Explanation

What would be some other way to explain these results? - maybe the people in the aerobics group just didn't feel as much stress to begin with. Maybe they were were less prone to stress than the aerobics people before the study even started. Maybe the aerobics people were just better at math than the weight-training people, and so the toughness of the math problem wouldn't be as intimidating to them.

Goal

Since this is Necessary Assumption, the correct answer will do one of two things: - rule out some other way to explain why the aerobics group has less measurable stress or - say something that is required for the author's explanation to make sense

21.

Which one of the following is an assumption the argument requires?

Three months is enough time
Too Strong: fully
In order for the author's story to be plausible, she does have to assume that "3 months is enough time for the body to benefit from aerobic exercise", because if it isn't enough time, then the aerobics class can't be the reason that the people in the aerobics group had less stress. But she doesn't need to assume that 3 months is enough for 100% of the benefits. Even if these people only had 90% of the benefits, that could still work for her story.
11% picked this
The volunteers who were assigned
Irrelevant Distinction
If the aerobics people did also lift weights outside of class, that wouldn't weaken the argument. It's not like we'd be able to say, "Hey, author, maybe it was the weight-lifting they did, not the aerobics class, that made them have less stress". That would be a nonsensical alternative explanation because the weight-lifting group obviously did weight-lifting, so if weight-lifting were the thing leading to lower stress then the weight-lifting group would have had comparable stress, not more stress.
32% picked this
On average, the volunteers who
Irrelevant Distinction
The author doesn't have to assume anything about "total exercise" for the aerobics group during the study vs. prior to the study. It wouldn't hurt the author if the aerobics group, prior to the study, go the same or more exercise as they did during the study. All the author needs to assume is that the aerobics group got more aerobic exercise during the study than the weight-lifting group did.
6% picked this
On average, the volunteers assigned
Weakens
This is the opposite of what we want. If this answer said, "on average, the aerobics people did not find it less difficult to do the math problem", we'd happily pick it. This answer as written is giving an Alternate Explanation for why the aerobics people had less stress. The author is assuming that the aerobics people found the math problem just as hard as the weight-training people did, but because of their (presumably) higher level of aerobics exercise (and because of the supposed idea that aerobic exercise helps the body handle stress), they showed less measurable stress symptoms.
13% picked this
Correct
On average, the volunteers assigned
Why this is right
If we negate this, it would weaken the argument. It would be saying, "the people in the aerobics group did not get more aerobic exercise during the study than the weight-training people did". That would blow up the plausibility of the Author's Explanation. The author is pitching "aerobic exercise" as the causal difference-maker that accounts for the lower stress symptoms of the aerobic group. But in order for some factor to explain the difference between two groups, it needs to actually be a difference between the two groups. If Jack got a 150 and Jill got a 160 on her LSAT, we can't say that "Jill's higher score was due to the fact that she read Logic Master", if Jack also read Logic Master.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
38% 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