Logical Reasoning · Weaken

PrepTest 151 · Section 3 · 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

When two things travel together and the argument says A causes B, show that B might cause A instead.

The basic logic

The argument links a measured level to a problem and decides the level is a cause. Pop it by flipping the arrow: if the problem itself raises the level, the link is explained without the level causing anything.

Tiny words that decide it

“factor causing”
“likely”
“rises when”

Playground logic

Marcus sees muddy bikes with flat tires and blames the mud. His patty is a link; his top bun is a cause. Owen pops it by showing the arrow can point the other way: flat tires make riders wobble into mud.

Step 2 · The kid story

Mud or Flat?

Marcus walks along the bike rack like a detective. "Every bike with a flat tire is covered in mud," he announces. "Mud makes tires go flat. Case closed." Owen kneels by a muddy bike. "Have you ever ridden on a flat tire?" he asks. "It wobbles. You can't steer. You slide right into the puddles by the gate." Lulu writes it down: Flat first, then mud? Priya nods. "If going flat is what sends kids into the mud, then the mud did not cause the flat. The flat caused the mud." Marcus frowns at the bike. "So my clue was pointing backwards?" "Like a sign on a one way street," says Kevin, who was eating pineapple pizza for some reason.

Step 3 · Try the model question

Bikes at the school rack that have flat tires turn up muddy far more often than other bikes. Riding through mud is known to leave dirt on tires. So riding through mud is probably a cause of flat tires.

Suppose each choice below is true. Which one does the most to undermine Marcus's argument?

Step 4 · The courtroom tale

The Squeaky Door Defense

A landlord sued a tenant. "Every apartment with a broken door hinge has a doormat soaked with oil," said his lawyer. "The oil wrecks the hinges!" Mr. Whitfield stood slowly. "Your Honor, when a hinge breaks, it squeaks terribly. What does a tenant do with a squeaky door?" He held up a can. "They pour oil on it, and it drips onto the mat." The judge raised an eyebrow. "So the broken hinge came first, and the oil came after?" "Exactly, Your Honor. The arrow points the other way." The landlord's lawyer stared at the can as if it had betrayed him.

Step 5 · Work the real question

Open PrepTest 151, Section 3, Question 20 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the conclusion: some factor that raises a level is a cause of a problem. Find the evidence: people with that high level have the problem more often. Ask whether the problem could come first. Look for the answer that shows the problem itself pushes the level up, which flips the arrow. Set aside answers about other illnesses, about reducing the level, or about who avoids the factor; they do not explain the link from the other side.