Unplugged Practice Test: Logical Reasoning Set 1, Question 25 (Weaken)
Taking the test? Finish it first. This page shows the answer.
- Weaken questions ask which new fact most undermines the argument.
- Find the gap the argument leaves open, then look for the choice that widens it.
- Every question on this test is original, written to the same logical skeletons as real questions, and Steve checked every one himself before release.
The question
Along the Sarrow estuary, two regional forms of the traditional fishing skiff developed over several centuries, with no single builder directing either. The open-water form has thick hull planking that shields the crew when the boat strikes floating debris, while the marsh form has thin planking. Thick planking adds weight, and weight is what limits how long a skiff can be built before it sits too low to clear the marsh shallows, so the marsh form is considerably longer. This indicates that against the debris in the marsh channels, a skiff's length is a better defense for its crew than thick planking would be.
25. Which one of the following, if true, most weakens the argument?
- (A)Marsh crews carry catches of a volume that only a skiff of the marsh form's length can hold without sitting too low to clear the shallows.
- (B)Skiffs with thick planking respond more slowly to the oar, which leaves their crews less able to steer around debris they see coming.
- (C)Skiffs of the marsh form meet debris in the channels about as often as skiffs of the open-water form meet debris in open water.
- (D)The two forms of skiff are rigged with sails of the same cut.
- (E)The open-water form of the skiff was in use for at least a century before the marsh form appeared.
AWhy (A) is correct
The argument reasons that because marsh skiffs run thin planking yet longer hulls, and thick planking shields the open-water crew from debris, length must work better than thick planking against debris in the marsh channels. That inference only holds if the marsh form's extra length exists to protect the crew. (A) knocks that out: if marsh crews need a hull that long just to carry their catch without sitting too low for the shallows, the length is explained by cargo capacity, not by any defensive edge over thick planking.
Why the other answers are wrong
BWhy (B) is wrong
(B) points to a real drawback of thick planking, slower steering around debris, which supports rather than undercuts the idea that length defends crews better.
CWhy (C) is wrong
(C) describes how often each form meets debris but doesn't show whether length or planking handles that debris better, so it leaves the argument standing.
DWhy (D) is wrong
(D) says nothing about hull weight, planking, or defense; matching sails is beside the point.
EWhy (E) is wrong
(E) is just a timeline of which form came first and doesn't touch whether length or planking protects a crew better.
Common questions
What type of question is this?
Weaken. Weaken questions ask which new fact most undermines the argument.
How do I get better at Weaken questions?
Find the gap the argument leaves open, then look for the choice that widens it. The free LSAT cheat sheet lists the wrong-answer patterns to watch for on every type.
