Logical Reasoning · Weaken

PrepTest 145 · Section 2 · Question 4

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

When a change is blamed on something that happened at the same time, another change in that window can steal the credit.

The basic logic

The argument sees a rise, notices a factor that changed over the same period, and names it the cause. Weaken by offering a different factor that also changed then and could explain the rise better.

Tiny words that decide it

“probably”
“by then”
“over that period”

Playground logic

Marcus says Saturday library crowds grew because the walls got painted a brighter color. That is a Rooster: same time, so it must be the cause. Pop it with another change in the same window, like the library starting free snack time.

Step 2 · The kid story

The Case of the Crowded Library

Five years ago, hardly anyone visited the town library on Saturdays. Now the place is packed with kids. Detective Marcus pulled out his magnifying glass. "Elementary," he declared. "During those five years, the library painted its walls a slightly brighter yellow. Bright walls attract kids. Case closed." Nadia raised one eyebrow. "Marcus, did anything else change in those five years?" Owen checked the library newsletter. "Huh. Four years ago the library started free snack time on Saturday mornings. Cheese crackers. Unlimited." Tommy, who had candy hidden in three pockets, said, "That would get ME there." Priya smiled. "Same window, much stronger reason. The paint might matter a little, but the crackers are a better suspect." Marcus slowly lowered his magnifying glass.

Step 3 · Try the model question

Five years ago, few kids visited the library on Saturdays; now many do. Over that time, the library painted its walls a slightly brighter color. So the brighter walls probably caused the bigger Saturday crowds.

Which choice, if correct, does the most damage to the argument?

Step 4 · The courtroom tale

The Case of the Packed Ice Rink

The rink owner's lawyer argued, "Ticket sales doubled over two years. During that time we replaced the old scoreboard with a shinier one. Clearly the scoreboard brought the crowds, and the scoreboard company deserves no bonus refund." Mr. Whitfield rose. "Your Honor, in that same two years, the town opened a train stop right outside the rink." He held up a map. "Before, families drove forty minutes. Now they ride five." The judge looked at the scoreboard photo, then at the map. "Counselor, a shiny scoreboard is nice. A train at the door is a far better reason for crowds. Your timing story just got a rival."

Step 5 · Work the real question

Open PrepTest 145, Section 2, Question 4 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Spot the Rooster: a change is blamed on another change that happened during the same period. Ask what else could have produced the change. Look for an answer that names a different factor operating in that same window that could plausibly explain the result. Skip answers about how noticeable things are, answers that show the change also happened elsewhere without linking a new cause, and answers that would make the result less likely.