Logical reasoning PrepTest 155 · Section 4 · Question 21

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Harrison → Pulham or Westerville
38% of students take night classes
29% of students who live in Westerville take night classes

Answer Anticipation:
Since every student at Harrison lives in either P or W, and fewer night students live in W than the average, more students than average who take night classes must live in P. Otherwise, where do all those night students live?

Answer Explanation:
This matches with our explanation. If fewer students take night classes than average in one dorm, then more than average must take them in the other, if those dorms are the only two options.

Key Takeaway:
The LSAT throws numbers at you to confuse you, making you think that you need to do math. That's not what the exam is testing. Rather, these questions tend to either be about the difference between percents and amounts (which this one isn't), or about overlapping sets, which this one is. You don't need to do math to figure out either of those!

Incorrect. Since all students live in either P or W, another way of saying this answer is, "More students who live in P take night classes than who live in W," since if more than half live in P, then fewer than half must live in W. However, if W has significantly more residents than P, W students could make up more than half of the night class population while still being a lower percent of W's residents. The percent here implies something about the relative population size!

Incorrect. Since we don't know how many students are living in P or W, we can't compare the number of students in each based on percents. That's a classic error of reasoning.

Incorrect. The stimulus is binary—you're either a student who takes at least one night class, or you're not. There's no information about students taking multiple night classes.

Incorrect. The LSAT is trying to get you to select this answer because night classes make up only a small fraction of classes, but 38% of students take one. However, without information about what percent of students take day classes, or the size of those classes, we can't infer this answer.