VIPLSATCracking LSAT makes you a VIP.

Logical Reasoning · Flaw

PrepTest 133 · Section 2 · Question 9

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type
Flaw
The one idea it tests
A gap between two groups can only close if one group moves and the other stays put. Watching just one side is a Bad Comparison.
The basic logic
The arguer sees that one group is currently doing better, notices that group's number is getting worse, and predicts the lead will vanish. Ask: what is the other group doing meanwhile? If it might be getting worse too, the lead could stay.
Tiny words that decide it
  • “rising”
  • “than”
  • “both”
  • “still”

Playground logic

Marcus looks at only one team in a two-team race. His patty: flashcard classes have fewer spelling mistakes, but their mistakes are climbing. His top bun: the lead will disappear, so drop flashcards. The secret sauce he forgot: the other classes are not climbing just as fast.

Step 2 · The kid story

The Flashcard Race

Ms. Rivera posted a chart. Classes that use spelling flashcards make fewer spelling mistakes than classes that do not. Marcus squinted at it like a detective. "Aha! Look, the flashcard classes made more mistakes this month than last month. Their lead will be gone soon. So the chart really proves we should throw the flashcards away!" Priya sipped her juice box. "Marcus, what about the classes without flashcards? Did their mistakes go up too?" Marcus opened his mouth. Then he closed it. Lulu flipped her clipboard. "Their mistakes went up even more," she said. "So the flashcard classes are still ahead." Marcus had watched only one runner and announced who would win the race. Biscuit barked, which everyone agreed was the dog version of "told you so."

Step 3 · Try the model question

Classes that use flashcards make fewer spelling mistakes than classes that do not. But mistakes are increasing in the flashcard classes, so this difference will soon disappear. Therefore, the evidence actually shows that flashcards should be dropped.

Marcus's reasoning is weakest because it

Choices

Step 4 · The courtroom tale

The Case of the Shrinking Lead

A fictional bakery fight. The prosecutor waved a graph. "Your Honor, Rosie's Rolls gets fewer burnt-bun complaints than the bakery next door. But Rosie's complaints are rising! Her lead is doomed, so her oven rules should be banned." Mr. Whitfield snapped his suspenders. "Lovely graph. Now show us the bakery next door." The prosecutor shuffled papers. "Their complaints are, um, rising faster." The judge sighed. "So Rosie is still ahead, and maybe pulling farther ahead. Counselor, you cannot tell me who wins a race by watching one runner." Case dismissed.

Step 5 · Work the real question

Open PrepTest 133, Section 2, Question 9 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the two groups being compared and which one is ahead now. Then spot the trend the arguer cites and notice it is about only one group. Ask what happens to the gap if the other group is moving the same way. The correct answer names that unchecked other side. Skip choices that describe moves the argument never makes, and choices about things the argument never claims.