Logical Reasoning · Weaken

PrepTest 142 · 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 contest scored on only one half of a job cannot crown a winner for the whole job.

The basic logic

Notice exactly what was counted. If the evidence counts only how many real cases each side caught, the conclusion ignores false alarms. An answer showing the loser does much better at the other half pops the argument.

Tiny words that decide it

“therefore”
“higher proportion”
“later confirmed”
“left to”

Playground logic

The Berry Beeper caught more of the ripe berries than Grandpa did, so Marcus says berry picking belongs to the Beeper. The patty only scores one half of the job. If Grandpa wins big at leaving the sour ones alone, the top bun wobbles.

Step 2 · The kid story

The Berry Beeper Showdown

Aunt Rosa bought a gadget called the Berry Beeper. It beeps at ripe strawberries. Grandpa, who has picked berries since forever, accepted the challenge. Lulu kept score. Of all the berries that turned out to be ripe, the Beeper beeped at more of them than Grandpa picked. "Victory!" yelled Marcus. "From now on, the Beeper picks every berry." Priya opened the basket. Half of the Beeper's berries were hard and green. "It beeps at almost everything," she said. "Of course it catches more ripe ones. It also grabs a pile of sour ones." Grandpa had left nearly every green berry on the vine. Lulu flipped her clipboard. "We only scored half the game." Marcus took a bite of a Beeper berry and made a terrible face.

Step 3 · Try the model question

In a contest, the Berry Beeper flagged a larger share of the strawberries that turned out to be ripe than Grandpa did. So all berry picking should be handed over to the Beeper.

Which of these, if true, does the most damage to the argument?

Step 4 · The courtroom tale

The Case of the Smoke Alarm Salesman

The salesman beamed. "Your Honor, in every house that truly caught fire, our new alarm went off more often than the old one. The town should install only ours." Mr. Whitfield rose, suspenders snapping. "May I ask how often it went off when there was no fire at all?" Silence. "Toast. Steam from a shower. Birthday candles," read Mr. Whitfield from a report. "Your alarm screamed at all of them. The old alarm stayed quiet." Judge Pines set down her pen. "So you counted the fires you caught and ignored the fires you invented. Half a scorecard is not a winning record."

Step 5 · Work the real question

Open PrepTest 142, Section 2, Question 20 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the exact measure the evidence uses and ask what part of the job it leaves out. Here, think about the cases that were not real positives. The best weakener shows the losing side does much better on that ignored part, so the overall winner is unclear. Skip answers that praise one side in vague terms, talk about the job in general, or hurt both sides equally.