Strengthen & Weaken Questions: LSAT & GMAT Practice Quiz
Strengthen and weaken questions are two sides of one skill: find the gap the argument leaves open, then decide whether an answer choice fills it or widens it. Together they are the most common pairing in LSAT Logical Reasoning and GMAT Critical Reasoning. Twelve drills below, five choices each. Read the stem carefully — half of these ask you to strengthen and half ask you to weaken, and the wrong-direction answer is always sitting right there.
0 / 12 answered
Q1
Residents of Halden who drink the town's tap water report fewer dental cavities than residents who drink only bottled water. Public health officials conclude that Halden's fluoridated tap water prevents cavities. Which of the following, if true, most weakens the officials' conclusion?
Q2
Ridgeway Manufacturing installed new safety equipment last year, and workplace injuries fell 40 percent. The plant manager argues the equipment caused the drop. Which of the following, if true, most strengthens the manager's argument?
Q3
A city council proposes doubling parking fees downtown in order to reduce traffic congestion. Which of the following, if true, most weakens the case for the proposal?
Q4
A study of 2,000 people found that those who reported feeling lonely were more likely to develop heart disease over the following decade. A commentator concludes that loneliness damages cardiovascular health. Which of the following, if true, most weakens the commentator's conclusion?
Q5
Brightpath Tutoring advertises that 90 percent of its students improve their exam scores. A skeptic argues that this statistic gives no reason to believe the tutoring is effective. Which of the following, if true, most strengthens the skeptic's argument?
Q6
The Meridian Hotel chain plans to convert half of its rooms to long-stay suites, reasoning that long-stay guests occupy rooms for more nights and will therefore raise annual revenue per room. Which of the following, if true, most weakens the chain's reasoning?
Q7
Ecologists want to restore the trout population in Lake Verrin. They note that trout numbers began falling the same year an invasive crayfish appeared, and they propose removing the crayfish. Which of the following, if true, most strengthens the proposal?
Q8
A newspaper reports that the city's new bike lanes have made cycling safer, citing that the number of reported cycling injuries has stayed flat since the lanes opened. Which of the following, if true, most weakens the newspaper's conclusion?
Q9
A pharmaceutical company argues that its new painkiller is safer than the leading brand, citing that fewer adverse events were reported for its drug last year. Which of the following, if true, most weakens the company's argument?
Q10
A school district introduced free breakfast at all its schools, and attendance rose the following year. The superintendent concludes that the breakfast program raised attendance. Which of the following, if true, most strengthens the conclusion?
Q11
A management consultant claims that open-plan offices reduce productivity, citing a survey in which 68 percent of open-plan workers said they found it hard to concentrate. Which of the following, if true, most weakens the consultant's claim?
Q12
Vintage vinyl records now outsell CDs at Harmony Records, so the store's owner concludes that her customers prefer vinyl to CDs. Which of the following, if true, most weakens the owner's conclusion?
Answer all 12 questions to see your result 👆
Strengthen & weaken: the cheat sheet
- Find the gap first
- Never read the choices cold. Name the jump between evidence and conclusion, then look for the choice that acts on that jump.
- Alternative cause
- The default way to weaken a causal claim: supply a different explanation for the same evidence. The default way to strengthen it: rule one out.
- Reverse the arrow
- Ask whether the supposed effect could be causing the supposed cause. Early illness causing withdrawal, not withdrawal causing illness.
- Control group
- The strongest strengthener for a causal claim is a comparable group that lacked the treatment and showed no effect.
- Rate vs. raw count
- Counts compared across groups of different sizes prove nothing. Look for the exposure figure hiding behind the number.
- Does the plan touch the cause?
- Weaken a plan by showing the problem comes from somewhere the plan never reaches.
- Wrong direction is the top trap
- Every weaken question hides a choice that strengthens, and vice versa. It will feel relevant because it is — just backwards.
- Popularity is not effectiveness
- That people dislike a plan, or that it costs a lot, does not show it will fail to work.
How strengthen and weaken questions work on the LSAT and GMAT
Strengthen and weaken questions give you an argument and ask which answer choice would make its conclusion more or less likely to be true. They are the most common pairing in LSAT Logical Reasoning and GMAT Critical Reasoning, and they are the same task run in opposite directions: locate the gap between the evidence and the conclusion, then decide whether a choice covers that gap or exposes it.
Because the two directions share a first step, the efficient way to study them is together. In practice the step that decides the question is not reading the choices — it is naming the gap before you read them. An argument that concludes a treatment worked because outcomes improved has a specific gap: something else might have improved them. Once you have named it, the correct choice usually announces itself, and the four wrong ones lose their pull.
The single most costly mistake is answering in the wrong direction. Test writers reliably include a choice that would be perfect if the stem had asked the opposite, and under time pressure it reads as obviously right. Circling the word 'strengthen' or 'weaken' in the stem before looking at any choice costs a second and prevents an entire category of error.
The second most costly mistake is treating relevance as impact. A choice can be about the same subject, be perfectly true, and still leave the conclusion exactly where it was. Cost figures, opinion polls and background history are the usual offenders. Ask of every candidate: if this were true, would the conclusion be any more or less likely? If nothing moves, it is not the answer, however on-topic it sounds.
Strengthen & weaken FAQ
What is the difference between a weaken question and a flaw question?
A flaw question asks you to describe what is wrong with the reasoning. A weaken question asks you to add a new fact that makes the conclusion less likely. Same gap, different job: describe it versus attack it.
Does the correct answer have to destroy the argument?
No. You are looking for the choice that most weakens or most strengthens, not one that settles the matter. Even a modest shift wins if the other four shift nothing.
Can a correct answer introduce new information?
Yes, and it usually does. Unlike assumption questions, strengthen and weaken answers are allowed to bring in facts the argument never mentioned.
How do I avoid picking the wrong-direction answer?
Mark the stem word before reading the choices, and restate your prediction as a direction: 'I want something that makes the plan fail' or 'I want something that rules out other causes.'
Are these real LSAT or GMAT questions?
No. Official questions are copyrighted by LSAC and GMAC. These are original arguments written in the style of both exams, using the same causal patterns and distractor traps.
Which is more common, strengthen or weaken?
Weaken questions appear somewhat more often than strengthen questions on both exams, but the pair together makes up a large share of Logical Reasoning and Critical Reasoning, which is why they are worth drilling early.