PrepTest 103

[lcid:3508] Prep Test 103 LSAT — Logical Reasoning — S1 Logical reasoning

Question prompt

When a planetary system Remaining source text redacted.
Why the credited answer is right

Credited answer: D

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

Argument Evaluation Questions

Stimulus Summary

When a planetary system forms: Chances of a planet that can support life are high Chances of a big planet are low Big planets protected Earth from large comets, without which intelligent life would never have formed Therefore - Chances of intelligent life are low

Answer Anticipation

Argument Evaluation questions aren’t very different from other flaw-based questions - the correct answer should highlight a piece of information that the argument is assuming. As such, we should be looking for an assumption of the argument! Here, the conclusion is that the chance of intelligent life is low. Why does it believe that to be the case? Because the chance of a large planet forming in a planetary system is low. But why does that matter? According to the stimulus, it’s because intelligent life wouldn’t have formed on Earth without the large planets in our solar system because they protected Earth from large comet strikes. However, there’s no indication that this would be a general problem for other planetary systems - maybe Earth’s solar system just has a lot more comets than others! In using what happened on Earth to show what must happen elsewhere, the argument is assuming that Earth’s solar system is representative as far as the connection between intelligent life, comets, and large planets is concerned. Let’s find an answer addressing that assumption.

Answer choices

  1. A
    whether all planetary systems Remaining source text redacted.
    Why choice A is not credited
    The argument does bring up large and small planets, but the total amount of matter in the planetary system is related to the size of the planets, the number of planets, and the mass of other bodies in the system. Since most of that is out of scope of the argument, so is this answer.
  2. B
    whether intelligent species would Remaining source text redacted.
    Why choice B is not credited
    This could be a tempting answer! However, there are two issues with it. First, we already know that life wouldn’t have survived on Earth if large comets frequently struck the planet. That’s several shifts on top of a statement that addresses this question partially. Second, this answer is about intelligent life surviving a comet strike, whereas the conclusion is about intelligent life forming. Even if a comet took out intelligent life, it still would have already formed.
  3. C
    whether large comets could Remaining source text redacted.
    Why choice C is not credited
    The premise leading directly into the conclusion is about the low chances of any (i.e., even a single) large planet from forming, even if a single planet would deflect comets, the chances of that forming are still low. While the chances of two forming would be lower still, since the chances of either situation is low, the argument could still hold together.
  4. D
    how high the chances Remaining source text redacted.
    Why choice D matches the stem
    This answer brings up the odds of a planetary system being similar to Earth is a key regard - the chances of containing many large comets. We know Earth’s solar system does, as many would have hit Earth without large planets around. If Earth is an outlier in that regard, then low planets may not be necessary for intelligent life to form; if it isn’t and the chances are very high that a planetary system will have many large comets, then those large planets would be necessary and thus the chances they form control the chances that intelligent life can form.
  5. E
    how likely it is Remaining source text redacted.
    Why choice E is not credited
    The size of Earth isn’t noted as being required for intelligent life, and we know that the chances a planet that can support life will form are high, so this is out of scope.

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