Logical reasoning PrepTest 103 · Section 1 · Question 9

Question prompt

Measurements of the motion 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

Weaken Questions

Stimulus Summary

Phenomenon - Uranus is being pulled away from the sun by a force that can’t be explained by Neptune and Pluto (the only two planets further away from the sun than Uranus) Explanation - There must be a planet further away from the sun than Uranus that we don’t know about

Answer Anticipation

First, Pluto is a planet - you can’t change our minds on that! Though it is funny to see these questions that have since become dated. This argument falls into a common pattern - the Phenomenon/Explanation pattern. A phenomenon is noted - the force pulling Uranus away from the sun. It rules out two things as a full explanation (Neptune and Pluto), and then the author puts forward an explanation - a planet that’s further away from Uranus that we don’t know about. When we’re dealing with a Phenomenon/Explanation argument where the main point is an explanation, we should start thinking about alternative explanations. And in a Weaken question, we weaken the argument by finding an answer that establishes a potential alternative explanation. Let’s head to the answer choices with that in mind.

Answer choices

  1. A
    Pluto was not discovered Remaining source text redacted.
    Why choice A is not credited
    When Pluto was discovered doesn’t bear on whether it could be exerting enough influence on Uranus to explain its motion.
  2. B
    There is a belt Remaining source text redacted.
    Why choice B matches the stem
    This answer brings up an alternative explanation - not another planet, but rather a belt of colts with a strong gravitational pull. This belt might be what’s exerting influence on Uranus, so it’s the correct answer.
  3. C
    Neither Neptune nor Pluto Remaining source text redacted.
    Why choice C is not credited
    The argument establishes that Neptune and Pluto can’t be the full story on the motion of Uranus, so their relative size compared to that planet doesn’t change anything. We don’t even know exactly how big the object needs to be that can explain Uranus’ motion.
  4. D
    The force the Sun Remaining source text redacted.
    Why choice D is not credited
    The inner planets aren’t really in scope here, and the argument is about something further from the Sun than Uranus.
  5. E
    Uranus' orbit is closer Remaining source text redacted.
    Why choice E is not credited
    How relatively close Uranus is to Pluto versus Neptune doesn’t change the fact that they can’t explain Uranus’s motion.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 5%
  2. B Credited 83%
  3. C 3%
  4. D 8%
  5. E 2%

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