Logical Reasoning · Flaw
PrepTest 150 · Section 2 · Question 1
Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.
Step 1 · Pre-Question Guidance · read this first
- “most”
- “my experience”
- “the ones who came”
Playground logic
Marcus says most kids love chess because everybody at chess club loves chess. His patty comes from kids who walked into chess club on purpose, but his top bun is about all the kids in school. That is a Weird Sample: the people who show up are not the people who stayed home.
Step 2 · The kid story
Marcus and the Chess Club Survey
Ms. Rivera mentioned that most kids at school find chess boring. Marcus gasped. "Wrong! I am a detective, and I have proof." Every Thursday Marcus goes to chess club after the last bell. Every Thursday, the twelve kids there cheer when a pawn becomes a queen. "See? Kids love chess!" Priya sipped her juice box. "Marcus, who goes to chess club?" "Kids who... like chess," he said slowly. "Right. Nobody drags themselves there. The kids who think it is boring are outside playing tag." Lulu wrote on her clipboard: twelve fans, three hundred kids, zero bored kids asked. Marcus frowned. "So my survey only visited the fan club." "Exactly," said Priya. "Ask the playground too."
Step 3 · Try the model question
Marcus: People say most kids at our school find chess boring. That is false. Every week I go to chess club, and every kid there is wildly excited about chess.
Which choice best describes the error in Marcus's reasoning?
Step 4 · The courtroom tale
The Case of the Happy Customers
"Your Honor," said the lawyer for Sparkle Skates, "the town claims most people dislike our skates. Nonsense! I spoke to every person at our Fan Appreciation Night, and all of them adored the skates." Mr. Whitfield snapped his suspenders and stood. "A question, counselor. Who comes to a Fan Appreciation Night?" "Well, fans." "And who stays home?" "People who... are not fans." The judge peered over her glasses. "So your survey visited only the people most likely to say yes. That sample picked itself. Show me what the rest of the town thinks, and then we can talk."
Step 5 · Work the real question
Open PrepTest 150, Section 2, Question 1 in your official copy from LSAC (for example in LawHub) and read it there.
Your answer
How to apply it
Read the argument and mark two groups: the group the evidence comes from and the bigger group the conclusion covers. Then ask how the smaller group got there. If its members chose to be there, or have a special reason to feel a certain way, the sample is weird. Look for the answer that names this mismatch in general terms. Skip answers about word meanings or values that the argument never uses.