LSAT 151 | Section 2 | Logical Reasoning: Q15

LR Question 15 Explanation

QUESTION TEXT: All the apartments on 20th Avenue are in old houses …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Most old houses on 20th Ave have more than one apartment.

REASONING: All the apartments are in old houses. But there are twice as many apartments as there are old houses.

ANALYSIS: Let’s say there are 10 old houses and 20 apartments. That sounds like enough to say most houses have more than one apartment. But what if:

• 2 old houses have 6 apartments each.
• 8 old houses have only 1 apartment.

Then there are still 20 apartments and 10 old houses, but most old houses don’t have more than one apartment.

So the flaw is that the argument assumes the apartments are spread out across the old houses. But we’re never told that. A small number of old houses could contain many apartments.

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1. It doesn’t matter whether some buildings on 20th Avenue aren’t old houses. The argument is only about apartments and old houses, and we’re told all apartments are in old houses.
2. Not circular reasoning. The conclusion isn’t just repeating a premise. It’s making a new claim about how apartments are distributed among old houses.
3. Other rental accommodations don’t matter. The argument is only about apartments, not rooms, condos, studios, halfway houses, etc etc.
4. It’s not confusing a necessary and sufficient condition.
5. CORRECT. Exactly. If a significant number of apartments are packed into a few old houses with three or more apartments, then most old houses might not have multiple apartments at all.