Hard LSAT Strengthen vs Weaken Questions Practice Questions

Concept Explanation

Strengthen and Weaken questions on the LSAT require you to identify the piece of new information that either increases or decreases the likelihood that an argument's conclusion follows from its premises. These question types are fundamental to the LSAT Prep curriculum because they test your ability to evaluate the relationship between evidence and claims. In a Strengthen question, you are looking for a fact that bridges a logical gap or eliminates a potential weakness. In a Weaken question, you seek a fact that exposes a flaw, provides a counterexample, or suggests an alternative explanation for the observed phenomena. Crucially, on the LSAT, you must accept the answer choices as true and determine which one has the most significant impact on the argument's validity.

To tackle these effectively, you must first isolate the conclusion and the premises. Most complex logical reasoning stems from an assumption—an unstated link between the evidence and the result. To strengthen the argument, find an answer that supports that assumption. To weaken it, find an answer that attacks it. Remember that "strengthen" does not mean "prove," and "weaken" does not mean "disprove." You are looking for the choice that moves the needle the most in the desired direction.

Solved Examples

1. Example 1 (Strengthen): A recent study found that residents of City X who own dogs are 20% less likely to suffer from heart disease than residents who do not own dogs. Therefore, the companionship provided by dogs directly improves cardiovascular health.
   Step-by-Step Solution:
   1. Identify the Conclusion: Dog companionship causes improved cardiovascular health.
   2. Identify the Gap: The argument assumes a causal relationship based on a correlation. It ignores potential "third factors" (e.g., dog owners might exercise more).
   3. Evaluate the Goal: We need to strengthen the causal link.
   4. Correct Answer: "A follow-up study showed that dog owners in City X do not engage in more physical activity on average than non-dog owners." This strengthens the argument by eliminating a major alternative explanation (exercise), making the companionship explanation more likely.
2. Example 2 (Weaken): The prehistoric site at Cave Y contains several charred bones of large mammals. Since these bones were found near primitive stone scrapers, it is clear that the inhabitants of Cave Y were skilled hunters of large game.
   Step-by-Step Solution:
   1. Identify the Conclusion: The inhabitants were skilled hunters of large game.
   2. Identify the Evidence: Charred bones and stone scrapers were found together.
   3. Identify the Gap: The evidence could be explained by scavenging rather than hunting.
   4. Correct Answer: "Microscopic analysis of the bones shows that the marks made by stone scrapers were applied over the teeth marks of large predators like lions." This weakens the argument by suggesting the humans were scavengers who processed carcasses left by other animals.
3. Example 3 (Strengthen): Company Z's new software significantly reduced the time employees spent on data entry. Consequently, Company Z will see an increase in overall profits this fiscal year.
   Step-by-Step Solution:
   1. Identify the Conclusion: Company Z will see an increase in profits.
   2. Identify the Gap: Reduced time on one task doesn't automatically mean higher profits; the cost of the software or loss of productivity elsewhere could offset gains.
   3. Correct Answer: "The cost of implementing the new software is less than the total savings generated by the reduction in employee labor hours." This strengthens the argument by addressing the financial viability of the change.

Practice Questions

1. Economists argue that the recent decrease in the unemployment rate is due to a surge in new small business startups. However, this cannot be the case, as the total number of small business licenses issued this year has actually declined by 10% compared to last year. Which of the following, if true, most weakens the argument?
2. A certain species of migratory bird has begun arriving at its nesting grounds two weeks earlier than it did twenty years ago. Biologists claim this is a direct result of rising global temperatures. Which of the following, if true, most strengthens the biologists' claim?
3. The city council plans to reduce traffic congestion by doubling the toll on the main bridge. They argue that the higher cost will discourage casual drivers, thereby freeing up the bridge for essential commuters. Which of the following, if true, most calls into question (weakens) the council's plan?

4. Studies show that children who play musical instruments perform better on standardized math tests than those who do not. Therefore, learning music enhances a child's mathematical reasoning abilities. Which of the following, if true, most weakens the argument?
5. A law firm found that its most successful associates are those who participated in competitive debate during college. To increase its success rate, the firm has decided to hire only former debaters. Which of the following, if true, most strengthens the firm's strategy?
6. The increase in the price of gold is often followed by an increase in the price of silver. Since gold prices rose sharply yesterday, silver prices will likely rise tomorrow. Which of the following, if true, most weakens the argument?
7. To reduce the incidence of theft, a retail store installed high-definition cameras in every aisle. Since the installation, the number of reported thefts has decreased by 30%. Thus, the cameras have been effective in deterring potential thieves. Which of the following, if true, most strengthens the argument?
8. Analysis of soil samples from Mars shows high concentrations of perchlorates, which are toxic to most Earth-based life forms. Therefore, it is highly unlikely that Mars ever supported microbial life. Which of the following, if true, most weakens the argument?

Answers & Explanations

1. Answer: The average number of employees per new small business startup is significantly higher this year than in previous years.
   Explanation: The argument concludes that startups aren't the cause of lower unemployment because the number of licenses is down. However, if each new startup is hiring many more people than before, the total impact on unemployment could still be positive despite fewer licenses. This is a common logic trap involving the distinction between totals and averages.
2. Answer: In the last twenty years, the primary food source for these birds has begun to emerge two weeks earlier due to the warmer climate.
   Explanation: This provides a specific mechanism (food availability) linked to temperature that explains why the birds would change their migration patterns, thus strengthening the causal link between temperature and arrival times.
3. Answer: There are no alternative routes or public transportation options available for the majority of commuters who use the bridge.
   Explanation: If drivers have no choice but to use the bridge, a higher toll will not discourage them. Instead, they will simply pay more, and congestion will remain unchanged, undermining the council's goal.
4. Answer: Children from high-income families are more likely to both take music lessons and have access to private math tutoring.
   Explanation: This identifies a "third factor" (socioeconomic status/tutoring) that could be the actual cause of the higher math scores, suggesting that the correlation between music and math is not necessarily causal.
5. Answer: The specific skills developed in competitive debate, such as rapid logical analysis, are the primary factors that contribute to success at the firm.
   Explanation: This strengthens the strategy by confirming that the debate experience itself—rather than an unrelated trait common to debaters—is what causes the success.
6. Answer: Yesterday's gold price increase was caused by a temporary shortage of gold ore that does not affect silver production or demand.
   Explanation: This weakens the argument by showing that the specific cause of the gold price hike is isolated and unlikely to trigger the usual silver price correlation.
7. Answer: A survey of the local community indicated that the presence of visible cameras was the most cited reason for individuals deciding not to shoplift at that store.
   Explanation: This provides direct evidence of the deterrent effect, linking the cameras to the behavior of potential thieves and supporting the causal conclusion.
8. Answer: Several species of bacteria discovered in Earth's extreme environments are known to thrive in soil with high perchlorate concentrations.
   Explanation: This weakens the conclusion by providing a counterexample; if life can exist in such conditions on Earth, the presence of perchlorates on Mars does not necessarily preclude the existence of life there.

Frequently Asked Questions

What is the difference between a Strengthen question and a Most Strongly Supported question?

In a Strengthen question, you look for a new piece of information in the answer choices that supports the passage's conclusion. In a Most Strongly Supported question, the passage acts as the evidence, and you must find an answer choice that follows logically from that evidence.

Can an answer choice be correct if it only strengthens the argument a little bit?

Yes, the correct answer only needs to strengthen the argument more than any other choice provided. It does not need to make the argument perfect or provide a complete proof of the conclusion.

How do I handle "Except" questions in Strengthen or Weaken formats?

In a "Strengthen EXCEPT" question, four choices will strengthen the argument, and the correct one will either weaken it or have no effect at all. Always treat these as an elimination game by marking the four that perform the task described.

Should I look for flaws in the stimulus before reading the answer choices?

Yes, identifying the logical gap or flaw in the stimulus is the most effective way to predict what a Strengthen or Weaken answer will look like. This proactive approach helps you avoid being misled by "shell game" answers that look relevant but don't address the core logic.

Do Weaken questions require me to prove the conclusion is impossible?

No, you only need to find the choice that makes the conclusion less likely to be true. Even a small piece of counter-evidence can be the correct answer if it casts more doubt than the other options.