Logical reasoning PrepTest 124 · Section 2 · Question 20

Incorrect. This answer is tempting! It sounds as if it suggests the author believes the first of the two statements is conditional, allowing the inference to be drawn. However, the conditional stated by this answer is Smog reaches unsafe levels → Hot days (necessarily accompanies" denoting a necessary condition), which still can't be combined with the other statement, so this answer is incorrect.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Hot days—some—Smog reaches unsafe levels
Hot days—some—Wind blows in from east
Therefore — Wind blows in from east—some—Smog reaches unsafe levels

Answer Anticipation:
While we're normally tasked with drawing inferences by combining quantifier statements, some questions on the LSAT will ask us to describe an argument that is flawed in that it draws an improper inference from quantifier statements.

Here, there are two some statements presented, and the conclusion draws an inference from them. However, two some statements can't lead to an inference because they're too weak to guarantee that members of the shared group overlap. If only 5% of hot days have smog reaching unsafe levels, and only 5% of hot days have the wind blowing in from the east, then there may be no days where both of those things happen.

Let's find an answer that highlights the statements are too weak to guarantee that the sets overlap.

Answer Explanation:
This answer describes the flaw in the argument. It correctly states that the argument fails to recognize that one set (hot days) may have some days in common with two other sets (unsafe smog levels; wind from the east) even if those two sets don't share any days in common. In concluding that those two sets do overlap—that they do have some days in common—the argument commits the flaw described here.

Key Takeaway:
Knowing your quantifier combination rules doesn't just help in Must be True questions! Those concepts can show up across question types, though they're most common in:
(1) Must be True
(2) Strengthen with Sufficient Premise
(3) Errors in Reasoning
(4) Flawed/Parallel Reasoning

Incorrect. There's no indication that the determination of unsafe smog levels is different in the premise than in the conclusion. This answer would be correct if, say, the premise were about smog levels unsafe for those with lung conditions and the conclusion were about unsafe smog levels for all people.

Incorrect. While this answer is phrased differently from the normal one, it still describes a circular argument. Since the conclusion isn't repeating a premise, it doesn't apply.

Incorrect. The entire argument is made up of correlations—the conclusion isn't causal.