LSAT 103 | Section 1 | Logical Reasoning: Q9

LR Question 9 Explanation

QUESTION TEXT: Measurements of the motion of the planet Uranus seem to…

QUESTION TYPE: Weaken

CONCLUSION: There must be another planet in our solar system.

REASONING: There is something tugging Uranus away from the Sun. Neptune and Pluto aren’t strong enough to do it.

ANALYSIS: The argument ignores the possibility that something outside the solar system or something that isn’t a planet is tugging on Uranus.

Pluto and Neptune were only mentioned to let us know that some other force was acting on Uranus. They aren’t otherwise relevant. A lot of the wrong answers mention those planets.

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1. This is completely irrelevant. Pluto is only mentioned to show that it isn’t strong enough to exert all of the force on Uranus.
2. CORRECT. It could be that comets are pulling on Uranus. Comets aren’t a planet.
3. So? We already know that Pluto and Neptune aren’t strong to generate all of the force pulling on Uranus. This just adds irrelevant information.
4. Of course. Uranus is farther away. But this doesn’t affect whether there must be another planet pulling Uranus the other way.
5. Pluto and Neptune aren’t relevant except for the fact that they aren’t strong enough to be exerting the force on Uranus.

Recap: The question begins with “Measurements of the motion of the planet Uranus seem to”. It is a Weaken question. Learn how to master LSAT Weaken questions on the LSAT Logical Reasoning question types page.