PrepTest 123

[lcid:3590] Prep Test 123 LSAT — Logical Reasoning — S3 Logical reasoning

Question prompt

When exercising the muscles Remaining source text redacted.
Why the credited answer is right

Credited answer: B

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Question Type

Strengthen with Necessary Premise Questions

Stimulus Summary

Muscles on both sides of the spine must pull equally to align and protect the spine, so balanced muscle development is necessary for a healthy back, so anyone exercising should make sure to exercise muscles on both sides of the spine equally to maintain a healthy back.

Answer Anticipation

First, the argument structure here can be a bit tricky. However, the second sentence starts with "After all . . . ", which generally is going to serve as a premise to what preceded it. The second half of that sentence starts with "since," telling us that what is before it is a conclusion supported by what follows. So we end with a premise that supports the first half of the second sentence, which itself supports the first sentence. In short, we have a main conclusion, then a subsidiary conclusion, then a premise.
This argument presents two things as necessary for maintaining a healthy back: equal pull from back muscles, and thus balanced muscle development. It uses these requirements to conclude that muscles on both sides of the back should be exercised equally. It sounds like good advice, but let's take a step back and look at the goal.
The goal is a healthy back. From the premises, we know this requires equal pull from both muscles and balanced muscle development. There isn't much of a gap between muscles that pull with equal strength and equal muscle development—if they're equally developed, they'll pull with equal strength. However, equal development doesn't necessarily require equal exercise—there's a gap between the intermediate conclusion and the main conclusion. Since the goal is equal muscle development, the goal should be to exercise both sides to be equally strong, which might require more of a focus on one side rather than the other. For example, maybe righties have a stronger set of right back muscles—they'd require more exercise on the left side to balance it out!

Answer choices

  1. A
    Muscles on opposite sides Remaining source text redacted.
    Why choice A is not credited
    Incorrect. The argument sets out several things as being necessary to maintaining a healthy back. This answer choice says that equally well developed back muscles are sufficient ("will be enough to"), which is a reversal of the logic in the stimulus.
  2. B
    Exercising the muscles on Remaining source text redacted.
    Why choice B matches the stem
    Correct. This answer choice deals with the connection between exercise and balance, so it's dealing with the gap we found in the logic. If unequal exercise doesn't tend to lead to unbalanced development, then the argument for equal exercise falls apart. If it does, then the argument holds together. This answer is necessary to reach the conclusion, so it's correct.
  3. C
    Provided that one exercises Remaining source text redacted.
    Why choice C is not credited
    Incorrect. This answer choice sets equal exercise on both sides of the back as sufficient to maintaining a healthy back, whereas the conclusion sets it up as important to doing so, which is closer to necessary than sufficient. In any case, this answer choice is stronger than the conclusion and a bit of a reversal, so it's not necessary.
  4. D
    If the muscles on Remaining source text redacted.
    Why choice D is not credited
    Incorrect. This answer choice is too strong in stating the damage would be irreparable. The conclusion sets up equal exercise as being important to maintaining a healthy back, whereas this answer is about irreparable damage. Even if unequal exercise led to repairable damage, the conclusion could still hold.
  5. E
    One should exercise daily Remaining source text redacted.
    Why choice E is not credited
    Incorrect. This answer is too specific. While equal exercise is important, there's no indication that daily exercise is necessary to maintaining a healthy back. Give those muscles a rest!

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