Logical Reasoning · Weaken

PrepTest 150 · 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

Weaken

The one idea it tests

A source that carries some bad items does not prove the buyer took the bad items.

The basic logic

The arguer sees that a supplier has some of the forbidden stuff and leaps to 'so the buyer's goods must include it.' Look for a fact that shows the buyer could easily pick only the allowed items from that mixed source.

Tiny words that decide it

“cannot be”
“some”
“all”
“no”

Playground logic

Marcus's patty: the art closet holds some permanent markers. His top bun: Lulu's box cannot be all washable. The secret sauce is that anything from a mixed closet must be mixed too, so we pop it by showing Lulu can tell the two kinds apart and grab only the good ones.

Step 2 · The kid story

The Closet Clue

Lulu taped a sign to her art box: 'Every crayon in here is washable!' Marcus squinted at it like a detective. "Impossible," he said. "You get your crayons from the supply closet in Room 4. I was in there yesterday. I saw a whole shelf of permanent markers. So your box can't be all washable." Lulu clicked her pen and checked her clipboard. "Marcus, the closet has two shelves. Every washable crayon in that closet has a big green sticker. I only take the green-sticker ones." Marcus opened his mouth, then closed it. Priya sipped her juice box. "Seeing bad stuff in the store," she said, "doesn't mean the bad stuff ended up in her basket. Not if she can tell which is which." Biscuit sniffed the box and found nothing permanent at all.

Step 3 · Try the model question

Marcus: Lulu says every crayon in her art box is washable, but that can't be true. She gets her crayons from the Room 4 supply closet, and I saw permanent markers on a shelf in that closet.

Suppose each answer below were true. Which would do the most damage to Marcus's reasoning?

Step 4 · The courtroom tale

The Case of the Glitter-Free Float

"Your Honor," said the prosecutor, "the parade club swears its float has no glitter. But the club buys supplies from Bunting Barn, and Bunting Barn sells buckets of glitter!" Mr. Whitfield snapped his suspenders and rose. "A fine shop sells many things," he said. "I submit Exhibit C: at Bunting Barn, every glitter-free item sits in an aisle with a giant purple sign. My clients shop only in that aisle." The judge nodded slowly. "So the shop having glitter does not mean the club bought glitter." "Exactly," said Mr. Whitfield. "A mixed store is not a mixed cart, if the shopper can spot which is which." The gavel came down. Case dismissed, and not a sparkle in sight.

Step 5 · Work the real question

Open PrepTest 150, 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 speaker's top bun: a claim that something cannot be fully clean or pure. Then find the patty: the buyer's source has some of the unwanted kind. Name the secret sauce: the buyer must have ended up with the unwanted kind. Now hunt for the choice that lets the buyer avoid it, such as a way to tell the two kinds apart at the source. Skip choices about other people's habits or about how harmful the bad items are.