PrepTest 103

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

Question prompt

Three–year–old Sara and her 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

Errors in Reasoning Questions

Stimulus Summary

Sara and Mike play together and have the same symptoms, so they probably have the same disease. Mike doesn’t have strep, so Sara doesn’t have strep.

Answer Anticipation

This argument has two Since statements, which tells us that it has a main point and an intermediate conclusion, and the flaw that shows up in the correct answer could reflect either of them. Let’s take them one step at a time. The first argument: Sara and Mike play together every day and have the same symptoms, so they probably have the same disease. Is this a valid argument? It is not. While playing together and having the same symptoms means that they very well might have the same disease, we can’t say that they “probably” do. So here, we have a conclusion that’s stronger than the premises supporting it. Second, the argument notes that they probably have the same disease, and so since Mike doesn’t have strep, neither does Sara. That also has a stronger conclusion than premise - them probably having the same disease doesn’t support that Sara definitely doesn’t have a disease since Mike doesn’t have it. Both of the conclusions in this argument make a jump between weaker premises and a strong conclusion, so let’s find an answer reflecting that.

Answer choices

  1. A
    presupposes what it sets Remaining source text redacted.
    Why choice A is not credited
    This answer describes a Circular Reasoning flaw, but the premises here are distinct from the conclusions.
  2. B
    mistakes the cause of Remaining source text redacted.
    Why choice B is not credited
    The argument does discuss causes and effects, but it doesn’t mix them up - it treats symptoms as the cause of the underlying disease.
  3. C
    fails to distinguish between Remaining source text redacted.
    Why choice C is not credited
    Different levels of strep are out of scope of the argument, as it doesn’t mention severity.
  4. D
    treats evidence that the Remaining source text redacted.
    Why choice D matches the stem
    This answer highlights the shift in certainty in the argument. Based on the two “probably” having different diseases, the argument concludes that one “definitely” doesn’t have a disease because the other doesn’t.
  5. E
    makes a general claim Remaining source text redacted.
    Why choice E is not credited
    The conclusion is about Sara - it’s not a general claim.

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