Logical Reasoning · Parallel Flaw
PrepTest 107 · Section 4 · Question 21
Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.
Step 1 · Pre-Question Guidance · read this first
- “many”
- “few”
- “at least one”
Playground logic
Marcus says lots of dino-lunchbox kids are in art club, and most art club kids play recess soccer, so at least one dino-lunchbox kid plays soccer. His sauce is that the two groups must overlap, but the dino kids might be the few art kids who skip soccer.
Step 2 · The kid story
The Dino-Lunchbox Soccer Theory
Marcus pointed his fork across the cafeteria. "Plenty of the kids with dinosaur lunchboxes are in art club. And almost every art club kid plays soccer at recess. So at least one dinosaur-lunchbox kid plays soccer. Science!" Kevin, clutching his own dinosaur lunchbox, looked worried. "I don't play soccer." Priya drew two circles on a napkin. "Art club is big. Most of it plays soccer. But a few don't. What if the dino kids in art club are exactly those few?" Lulu checked her clipboard. "All four dino kids in art club spend recess painting rocks." Kevin relaxed. "I paint a stegosaurus on mine." Marcus put his fork down. "Fine. Groups overlapping with a middle group don't have to overlap with each other."
Step 3 · Try the model question
Many of the kids with dinosaur lunchboxes are in art club, and hardly any art club kids skip recess soccer. So at least one kid with a dinosaur lunchbox plays recess soccer.
Which argument below has a flaw most like the one in Marcus's argument?
Step 4 · The courtroom tale
The Case of the Missing Trumpet Player
The prosecutor declared, "Many members of the Chess Society are also in the Night Owls Club, and nearly all Night Owls play trumpet. Therefore at least one Chess Society member plays trumpet, and so one of them made that noise at midnight!" Mr. Whitfield snapped his suspenders. "Your Honor, nearly all is not all. The handful of Night Owls who do not play trumpet could be exactly the chess players." He handed up a list. Every chess-playing Night Owl played the tuba, quietly, at noon. The judge nodded. "Two groups each touching a middle group need not touch each other. Next case."
Step 5 · Work the real question
Open PrepTest 107, Section 4, Question 21 in your official copy from LSAC (for example in LawHub) and read it there.
Your answer
How to apply it
Turn the argument into letters and quantity words: some, most, few, all, none. Note the conclusion claims an overlap between the first and last groups. Ask whether the premises truly force that overlap. Then translate each choice the same way. The right one has a matching chain and the same unforced overlap. Drop choices that are valid or that commit a different kind of error.