LR Question 21 Explanation
QUESTION TEXT: All of the students at Harrison University live in one of two…
QUESTION TYPE: Must be True
FACTS:
- All of the Harrison students live at either Pulham or Westerville.
- A small fraction of the classes at Harrison are night classes.
- 38% of Harrison students take at least one night class.
- Only 29% of Harrison students living in Westerville take at least one night class.
ANALYSIS: Looking at the facts, it looks like we’ll get an answer about what is true for some or all of a group of people. Every one of our facts deals with a specific portion of something being a certain way.
We learn that everyone either lives in Pulham or Westerville. That means that 38% of people who live in either Pulham or Westerville are taking a night class. Because Westerville is below that average, Pulham must be higher than the 38% average. This is true no matter how many students are in each residence.
___________
- CORRECT. See above.
- This isn’t necessarily true. It could be that Pulham has far fewer students in total, but a higher proportion of its students take night classes.
- We don’t know this. We just know that Westerville has a lower percentage of night class students.
- We really don’t know anything about who takes more than one night class. Everything we have tells us who takes at least one.
- We don’t have anything to base this on. We know that 38% of students take at least one night class, but they’re probably in several day classes as well.
Recap: The question begins with “All of the students at Harrison University live in one of two”. It is a Must be True question. Learn how to master LSAT MBT questions on the LSAT Logical Reasoning question types page.
More Resources for Must Be True Questions
- Conditional Reasoning Article: Learn about conditional statements on the LSAT.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Intro to Conditional Reasoning: This intro course lesson covers conditional reasoning basics.
- Intro Course lesson: This intro course lesson covers Must Be True questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers must be true questions.
Hi Graeme/LSATHacks team, thanks for this. I wanted to expand on B as I’m a bit confused. Wouldn’t it be that Pulham could have a much higher amount of students than Westerville and a lower proportion?
Just to conceptualize this lets say Harrison has 1100 students split into Westerville (100) and Pulham (1000). 29 students in Westerville take night classes (29%). A total of 418 students at Harrison take night classes (38%). This means that in Pulham there are 389 students who take night classes (or 38.9%) of students at Pulham.
Appreciate any insight you can give on this. Thanks for all your work and responses!
Hi Amaresh! I’m glad to hear that you’re enjoying the site.
Let’s break down why B is not correct and clarify the logic. It claims that more than 50% of the students are from Pulham. As your hypothetical shows, this CAN be true. But we’re looking for an answer that MUST be true.
If we adjust the numbers so that Pulham has a smaller population, let’s imagine that Harrison has 1000 students with 700 in Westerville and 300 in Pulham. This means that 380 student sin total take night classes (38%). For Westerville, this would mean that 203 students take night classes (29%). If we subtract 380 – 203 to get the number for Pulham, this laves us with 177 students from Pulham with night classes.
B says that more than 50%, so more than half, of the total students in night classes live in Pulham. However, 177 is only 46.6% of 380. So it’s not more than half.
Essentially, you wrote out a potential scenario that allows B to be true in line with the stimulus. But as exemplified by my hypothetical, we can also write out a scenario that follows the rules of the stimulus, but where B is not true. So B doesn’t HAVE to be true. That’s what Graeme is getting at in the explanation: if Pulham has fewer students than Westerville, we get a scenario (like the one I wrote out) where less than 50% of the total students taking nightclasses live in Pulham.
Hopefully that clarifies your confusion!