LSAT Logical Reasoning : Determining the flaw in the argument

Study concepts, example questions & explanations for LSAT Logical Reasoning

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Example Questions

Example Question #21 : Flaw

Therapists who treat patients for long periods of time develop attachments to the patients.  Once such attachments are formed, they are unable to take an objective view of the patients’ symptoms, leading to possible bias and inaccuracy in their diagnoses and treatment.  Therefore, to improve the quality of their treatment, patients should switch therapists every three to six months.

The reasoning in the argument is most vulnerable to criticism on the grounds that the argument fails to consider the possibility that

Possible Answers:

it is more expensive to switch therapists every three to six months than it is to remain with the same therapist for a long period of time

the quality of a patient’s treatment is often determined by the therapist rather than the patient

long-term relationships between therapists and patients create benefits in the quality of treatment which outweigh the possible negative consequences of attachments

most inaccuracies in diagnosis or treatment do not necessarily prevent the patient from continuing to progress therapeutically

not every therapist develops a strong attachment to every one of his or her patients

Correct answer:

long-term relationships between therapists and patients create benefits in the quality of treatment which outweigh the possible negative consequences of attachments

Explanation:

The argument’s conclusion states that patients should switch therapists to improve the quality of their treatment, but fails to indicate that the possible bias and inaccuracy resulting from attachments to patients necessarily leads to lower quality treatment.  Hence, it is possible that long-term relationships create benefits which outweigh the negative consequences mentioned.  The remaining answer choices are either irrelevant or attack the argument’s premises rather than its reasoning and conclusion.

Example Question #21 : Determining The Flaw In The Argument

Theme park executive: While normally our park closes at 9:00 pm, we recently experimented by leaving it open until midnight for a period of one week.  We did not expect a significant increase in traffic during nighttime hours.  To our surprise, on each day during that week the park was more crowded between 9:00 pm and midnight than it was during any other three-hour period.  Therefore, to maximize our attendance, we should leave the park open until midnight all year long.

The reasoning in the theme park executive's argument is flawed on the grounds that it

Possible Answers:

overlooks the possibility that the experiment's novelty, rather than the operating hours themselves, was responsible for the observed attendance

presumes, without providing justification, that those who remained in the park during the later hours would not have left had the park closed earlier

takes for granted that late-night attendance will remain constant during all seasons of the year

confuses a condition merely necessary for the observed effect to occur for a condition sufficient to cause the observed effect

draws a conclusion regarding theme park attendance that merely restates one of the argument's premises

Correct answer:

overlooks the possibility that the experiment's novelty, rather than the operating hours themselves, was responsible for the observed attendance

Explanation:

There is a possible explanation for increased attendance during the late hours which is completely overlooked by the theme park executive: namely, that the late hours only occurred for a week.  In other words, it is quite possible that attendance was high during those periods because attendees saw this as a special, one-time event (the equivalent of a product being available "for a limited time").  If the late hours became a permanent fixture of the theme park, the novelty might wear off and there is no indication that attendance would remain high in those circumstances.  The argument does not assume that late-night attendance will remain constant throughout the year; rather, it assumes it will remain high enough to be profitable.  The remaining answer choices do not accurately describe the argument's reasoning.

Example Question #21 : Determining The Flaw In The Argument

Art history books are always written using elaborate language.  Economics books are always written using unsophisticated language. Amanda’s professor wrote a book about the economics of art history. Therefore, the book uses moderately elaborate language.

Which answer choice uses the same flawed reasoning that is used in this example?

Possible Answers:

Chihuahuas are dogs that always have high-strung personalities. Corgis are dogs that always have mellow dispositions. Taylor has a dog that is a mix between a Chihuahua and a corgi. Therefore, Taylor’s dog has a moderately high-strung personality. 

People who go fishing always live along the coast. People who go hunting always live in rural areas. John has property both along the coast and in a rural area. Therefore, John both goes fishing and hunting. 

Women who shop at department stores always wear expensive clothing. Women who shop at thrift stores always wear inexpensive clothing. Therefore, women who shop at both department stores and thrift stores wear both expensive and inexpensive clothing. 

Email is delivered more quickly than post mail. Post mail is more personal than email. Arnold scanned a letter that he received as post mail and then delivered it to his father using email. Therefore, the email that Arnold sent is both personal and was delivered quickly. 

Dresses that are made from cotton are always comfortable. Dresses made from nylon are usually uncomfortable. Andrea bought a dress that is mostly made from cotton, but includes some nylon. Therefore, the dress is mostly comfortable. 

Correct answer:

Chihuahuas are dogs that always have high-strung personalities. Corgis are dogs that always have mellow dispositions. Taylor has a dog that is a mix between a Chihuahua and a corgi. Therefore, Taylor’s dog has a moderately high-strung personality. 

Explanation:

The flawed reasoning follows the pattern that if “A” always has quality “X” and if “B” always has the opposite of quality “X,” then something that is a mix of “A” and “B” will have a moderate amount of quality X.

 

In the example, “art history books” (=A) always has the quality of “using elaborate language” (=X) However, “economics books” (=B) do not. Therefore, a mix of art history books and economics books (A + B) would use a moderate amount of (X), elaborate language.

 

In the correct answer, this same reasoning is followed.

 

Chihuahuas = A

Corgis = B

High-strung personalities = X

Example Question #1 : Critical Reasoning

Advertisement: Coma Cola is the best-tasting cola on the market and we conducted a test using over 1000 cola consumers to prove it. Each consumer was given two identical cups filled with a carbonated beverage from the same fountain. One cup was filled with Coma Cola and the other was filled with unadulterated soda water. Ninety-nine percent of the consumers preferred the Coma Cola. So, Coma Cola is the best tasting cola available.

The advertisement’s reasoning is most vulnerable to criticism on the grounds that it fails to consider whether ___________________

Possible Answers:

Any portion of the population is allergic to any of the ingredients in Coma Cola.

The consumers tested had the opportunity to evaluate flavored soft drinks other than colas.

Coma Cola is cheaper or more expensive than other colas.

The consumers tested had the opportunity to evaluate colas other than Coma Cola.

Coma Cola has more or less caffeine than other colas.

Correct answer:

The consumers tested had the opportunity to evaluate colas other than Coma Cola.

Explanation:

The advertisement's claim, that Coma Cola is the best tasting cola, is based on 99% percent of cola consumers choosing it over soda water. The flaw in the experimental setup is that just because a consumer chooses Coma Cola over soda water, it does not mean that she will choose Coma Cola over any other cola, let alone over all other colas. 

The correct answer recognizes that, in order to validly make such a claim, one would have to show a preference for Coma Cola over other colas, not over soda water (or even over other flavored soft drinks, as one of the incorrect answer choices indicates).

Example Question #21 : Determining The Flaw In The Argument

Students that drink green tea while studying have higher test scores than those that drink soda while studying. Tea manufacturers emphasize that students who reported drinking green tea while preparing for a test achieved consistently higher test scores than those students who reported drinking soda while preparing for the same test. If this claim is true, then if the students who drink soda switched to drinking green tea, their test scores will rise.

The reasoning in this argument is flawed because the argument

Possible Answers:

accepts the conjecture without challenge that green tea is healthier for students than soda

utilizes an unsupported assumption that soda lowers the IQ of students

does not provide the precise percentage rise in scores of drinking green tea

fails to consider the cost difference between a cup of green tea and a can of soda

ignores the possibility that students who drink green tea may have other characteristics besides their drink preference that yield to higher test scores than those students who prefer to drink soda

Correct answer:

ignores the possibility that students who drink green tea may have other characteristics besides their drink preference that yield to higher test scores than those students who prefer to drink soda

Explanation:

The author, here, makes the mistake of assuming that drinking green tea raises test scores or that conversely, drinking soda yields lower test scores. Therefore, the author ignores the possibility that there may be other characteristics besides drink preference that determines a test taker’s score. Thus, the correct choice is “ignores the possibility that students who drink green tea may have other characteristics besides their drink preference that yield to higher test scores than those students who prefer to drink soda.”

Example Question #21 : Determining The Flaw In The Argument

Everyone who achieves success must struggle first. Seth has achieved success. Therefore, Seth must have struggled first.

If the author's premise is to be taken as true, what is the flaw in the author's argument?

Possible Answers:

Seth may have achieved success first and struggled later.

Not everyone will both struggle and achieve success.

There is no flaw in the argument.

Seth may achieve success without ever struggling.

Not everyone who struggles will eventually achieve success.

Correct answer:

There is no flaw in the argument.

Explanation:

If the author's premise is true, then there is no flaw in the author's argument. The premise states that everyone who achieves success must struggle first. Therefore, if the premise is true, it is logical to conclude that if Seth has achieved success, he must have first struggled.

Example Question #21 : Determining The Flaw In The Argument

Criminal trials that are tried before a jury end up in guilty verdicts two out of every three times, while trials that are tried before a judge end up in guilty verdicts three out of every four times. Therefore, a criminal defendant has a better chance of receiving a not guilty verdict if he elects to try the case before a jury (made up of jurors) instead of a judge.

Which of the following is a flaw in the argument?

Possible Answers:

Judges have a better understanding of the law than jurors.

Jurors tend to be more emotional than judges.

Both judges and juries find more defendants guilty than they find defendants not guilty.

Juries deliver longer sentences for guilty defendants when compared to judges.

Several variables affect whether defendants elect a judge or jury trial.

Correct answer:

Several variables affect whether defendants elect a judge or jury trial.

Explanation:

The flaw in the argument is best represented by the choice that several variables affect whether defendants elect a judge or jury trial. These variables could influence if a defendant is found guilty or not. For example, defendants who are guilty but who wish to receive shorter sentences may elect the forum in which that is more likely. This could skew the results for guilty verdict rates. None of the other choices represent a flaw in the argument.

Example Question #22 : Determining The Flaw In The Argument

Economist: Recessions are a natural part of any economy, as no advanced nation has ever experienced a significant length of time without slight bumps. The serious fretting over economic downturns is silly, as economic booms are right around the corner. Even if people lose some of their money, it should come back.

Politician: Any economic suffering a person has is something that should be avoided. Preventing even the smallest recessions is a priority that anyone with a responsibility for the economy must have.

The flaw in the economist’s argument would be stated by the politician as __________.

Possible Answers:

creating a false sense of panic over economic recessions

misunderstanding why economic recessions happen

overstating the need for economic action

emphasizing the problems with a recession to an economy

underestimating the effect of a recession

Correct answer:

underestimating the effect of a recession

Explanation:

The politician does not directly criticize the economist, but rather presents a viewpoint about avoiding economic recessions because of the pain it could cause people. The economist's argument is that the effect of an economic recession is not that serious, which the politician would say is minimizing the effects of the recession.

Example Question #23 : Determining The Flaw In The Argument

University Dean: These accusations of grade inflation at our university are untrue. A recent survey of our students proves that students are always graded fairly, because 93% of former students responding said that they had always been graded fairly in their courses here.

The flaw in the dean's argument is that it:

Possible Answers:

Does not define the word "fairly."

Justifies a claim based on unverifiable evidence.

Assumes that grading methods were different for former students compared to grading methods for current students.

Generalizes based on a sample that might not be representative.

Presents an initial claim that is true only if one assumes that the conclusion is true.

Correct answer:

Generalizes based on a sample that might not be representative.

Explanation:

The dean uses a survey of former students about the fairness of grading processes to justify his argument that grades are not artificially inflated at his university.  He does not provide any information about the sample size of the survey, uses former students rather than current students, and generalizes that the university's entire grading practices are "fair" based on this sample.

Example Question #191 : Lsat Logical Reasoning

The candidate with the most screen time in a televised debate usually receives the largest poll bump. As Mr. Smith received ten percent more screen time in the most recent debate, he should see a significant improvement in his poll numbers.

Which of the following statements best describes the flaw in the argument presented in the above passage?

Possible Answers:

That the debate was focused on serious issues that voters most care about.

That all politicians feature the same talking points in debates.

That most politicians focus on winning debates as compared to the other aspects of campaigning.

That the use of poll numbers is always reflective of actual opinions and beliefs.

That an event which has occurred in the past is guaranteed to occur in the future.

Correct answer:

That an event which has occurred in the past is guaranteed to occur in the future.

Explanation:

The passage states that Mr. Smith will see a jump in his poll numbers, because he had the most screen time during a debate. The only evidence for this conclusion was that the candidates whose poll numbers had most improved were the ones who had gotten the most screen time in previous debates. This would be the biggest flaw in the statement. Also, just because the candidates saw the biggest relative improvement, does NOT mean that the leap to calling this potential bump in numbers as significant.

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