Logical Reasoning · Flaw

PrepTest 111 · Section 3 · Question 13

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

The arguer attacks a current rate by pretending that rate must have been running for a very long time.

The basic logic

Patty: there were never more than a fixed number of items, and few new ones arrive. Top bun: a claimed loss rate must be exaggerated, because at that rate everything would be gone long ago. The hidden move: treating a claim about the pace now as a claim about the pace for years. Name that time stretch.

Tiny words that decide it

“now”
“long ago”
“never more than”

Playground logic

Marcus says the lunchroom can't be losing five forks a day, since there were never more than two hundred forks, so they'd all be gone long ago. His secret sauce is that the five-a-day pace has been going on for months or years, when it may have started only recently.

Step 2 · The kid story

Marcus and the Vanishing Forks

Lulu reported to the student council. "By my count, the lunchroom is losing about five forks a day." Marcus scoffed. "Way too high, Lulu. We all know nobody has bought new forks in ages. But the lunchroom never had more than about two hundred forks. At five a day, they'd all have disappeared months ago!" Priya sipped her juice box. "Marcus, Lulu said forks are disappearing that fast now. She didn't say it's been happening all year." "Oh," said Marcus. Nadia raised her hand. "Actually, it started two weeks ago, when the new art teacher started using forks for clay." Biscuit, who had wandered into the meeting, had a fork in his mouth. Nobody asked.

Step 3 · Try the model question

Lulu says the lunchroom is losing about five forks a day. Marcus: That number is way too high. No new forks have been bought in ages, and the lunchroom never had more than about two hundred forks. At five a day, the bins would be empty by now.

Marcus's reasoning is weakest because it

Step 4 · The courtroom tale

The Case of the Thinning Library

In a fictional courtroom, a library board accused a reporter of lying. "The reporter claims we lose ten books a week to unreturned loans," said their lawyer. "We have never owned more than three hundred books. At ten a week, the shelves would have been bare years ago!" Mr. Whitfield stood, smiling. "Your Honor, my client wrote that the library is losing ten books a week now. She never said that pace started years ago. The new loan rules began last month." The judge set down her pen. "Counsel, you multiplied a fresh pace by an old calendar. Motion denied."

Step 5 · Work the real question

Open PrepTest 111, Section 3, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the claim being attacked and notice its time frame: it describes a pace right now. Then find the arguer's math, which needs that pace to have run for many months. Prephrase the flaw as stretching a present rate across the past. Check each choice for that time-frame mix-up. Reject choices that describe moves the arguer never makes (Phantom Piece), even if they sound like real flaws.