LSAT 151 | Section 3 | Logical Reasoning: Q21

LR Question 21 Explanation

QUESTION TEXT: In an experiment, some volunteers were assigned to take …

QUESTION TYPE: Necessary Assumption

CONCLUSION: Aerobic exercise helps the body handle stress.

REASONING: During a math challenge, people who took aerobics were less stressed than people who did weight-training.

ANALYSIS: Aerobic exercise just means cardio. You get cardio from walking to work, shopping, going up the stairs, dancing.

What if people who did weight-training also got the same amount of aerobic exercise? If that was the case, then the difference in stress symptoms could not fairly be attributed to aerobic exercise.

So we need to know that the aerobics group actually got more aerobic exercise overall than the weight-training group.

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1. The argument doesn’t require that three months gives the full benefit of aerobic exercise. It only needs aerobic exercise to have some effect.
   Negation: Three months is not enough time for the body to fully benefit from aerobics.
2. The aerobics volunteers could have lifted weights outside class and the argument could still work. What matters is whether they got more aerobic exercise.
   Negation: The aerobics volunteers lifted weights outside the classes.
3. This compares the aerobics group to their own past exercise habits. But the argument depends on comparing the aerobics group to the weight-training group.
   Negation: The aerobics volunteers got less exercise than they did before the experiment.
4. This would weaken the argument. If the aerobics group found the math easier, maybe their lower stress was due to the task being less difficult, not aerobic exercise.
   Negation: The aerobics volunteers found the math more difficult than the weight-training volunteers.
5. CORRECT. This is required. If the aerobics group didn’t do more aerobic exercise overall than the weight-training group, then the experiment would not support the claim that aerobic exercise caused the lower stress response.
   Negation: The aerobics volunteers did not get a greater amount of overall aerobic exercise than the weight-training volunteers.