Logical Reasoning · Weaken

PrepTest 129 · Section 2 · Question 20

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 before-and-after drop is credited to one change, so another change at the same time can pop it.

The basic logic

The top bun says the new rule caused the drop. The secret sauce is that nothing else changed in that window. Look for a different cause that showed up in the same years and could make the numbers fall on its own.

Tiny words that decide it

“since”
“thus”
“at least”
“reduced”

Playground logic

Marcus says the new sign caused fewer dropped trays (Rooster logic: the sign came first, so it gets the credit). Priya pops it by pointing to new grippy trays that arrived at the same time. Another cause in the same window weakens the claim.

Step 2 · The kid story

The Great Tray Mystery

For years, the cafeteria had more and more dropped lunch trays. Splat, splat, splat. Then Ms. Rivera hung a big sign: WALK SLOWLY WITH YOUR TRAY. Since then, dropped trays have been way down every single month. Marcus put on his detective hat. 'Case closed! The sign cut the drops!' Priya sipped her juice box. 'Maybe. But do you remember what else came that same week?' Marcus blinked. 'The new trays,' said Nadia. 'The ones with rubbery grips on the sides. You basically can't drop them.' Owen added, 'Even Kevin hasn't dropped one, and he carries his tray with one hand while talking about dinosaurs.' Marcus took off his hat. 'So the sign might not have done much at all.' Biscuit, waiting outside for fallen fries, looked very disappointed.

Step 3 · Try the model question

Before the cafeteria sign went up, dropped trays rose every year. Since the sign went up, dropped trays have been much lower every month. So the sign reduced dropped trays.

Which choice, if true, does the most damage to this reasoning?

Step 4 · The courtroom tale

The Scarecrow Defense

A farmer sued a scarecrow maker, demanding a bonus. 'Before the scarecrow, crows ate more corn every year,' the farmer told the court. 'Since the scarecrow, crows eat far less. The scarecrow did it, so I owe him nothing extra... wait, I mean he owes me!' Everyone looked confused. Mr. Whitfield stood up for the scarecrow maker's rival. 'Your Honor, the very same spring, the farmer also put up nets over every row.' The courtroom gasped. 'The nets alone could keep the crows away. So we cannot hand the scarecrow all the credit.' The judge nodded. 'A second change in the same window. Very tidy, counselor.'

Step 5 · Work the real question

Open PrepTest 129, Section 2, Question 20 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Name the change the argument credits and the time window it compares. Then ask: what else could have changed in that same window? Hunt for a choice that brings in a separate cause able to lower the numbers on its own, starting around the same time. Skip choices about how people felt, choices about the period before only, and choices that would make the credited change look even better.