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 #31 : Flaw

Drivers often believe that a lane that is closed for roadwork is one to be avoided if the problem is to be passed more quickly. However, being in the lane which is merging often means cars are moving more and create motion which allows the lane to be faster overall. Additionally, the swarm of cars moving out of the lane and into others causes problems with the other lanes of traffic.

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

Possible Answers:

The argument relies on an assumption that is not sufficiently supported.

The argument does not present a conclusion based on any evidence.

The argument is presented based on incomplete evidence.

The argument is based on an assumption that is denied in other parts of the statement.

The argument presents two very different pieces of evidence to support its conclusion.

Correct answer:

The argument presents two very different pieces of evidence to support its conclusion.

Explanation:

The statement presents its conclusion in its opening statement, but then presents its reasons afterwards; however, the passage oddly makes two different statements that are not entirely congruent together, and even make somewhat conflicting arguments.

Example Question #31 : Determining The Flaw In The Argument

Tad and Lilly play together in kindergarten every day. Both children have symptoms of an illness. Tad definitely does not have an illness. Lilly’s illness symptoms are similar to Tad’s symptoms. Since Tad does not have an illness, Lilly does not have an illness.

The reasoning in the argument is flawed because the argument:

Possible Answers:

Wrongly infers that, because something in one instance has not occurred, it has not occurred in a similar situation.

Treats symptoms as facts.

Does not reason that one infection might be a different kind of illness.

Makes a general claim where specific facts are needed.

Argues that because something is probably true, it is true.

Correct answer:

Wrongly infers that, because something in one instance has not occurred, it has not occurred in a similar situation.

Explanation:

The flaw in the argument is that Tad’s situation and Lilly’s situation are the same simply because they play in kindergarten together every day. While the evidence that they play in kindergarten is compelling at first and may lead one to select one of the other false answers, it is flawed because it is not certain. The symptoms, even if similar, could be for something else. The question does not provide us with information concerning other illnesses which might have the same symptoms.

Example Question #32 : Determining The Flaw In The Argument

Brianna: Laura claims that her phone battery dies too quickly because I dropped her phone on the floor.  However, she also admitted that her phone battery died too quickly on many other occasions, despite never having been dropped on the floor on those occasions. Therefore, Laura is wrong in claiming that I caused her quickly dying battery by dropping the phone on the floor.

The reasoning in Brianna's argument is most flawed in that it: 

Possible Answers:

Fails to consider that even though the battery died quickly in the past without the phone having been dropped, dropping the phone could still be a cause of a quickly dying battery in this case.

Does not consider the possibility that dropping the phone caused the screen to crack.

Assumes that her claim is true without any evidence.

Doesn't consider the possibility that dropping any phone would cause its battery to die quickly.

Assumes that Laura is blaming her for dropping the phone.

Correct answer:

Fails to consider that even though the battery died quickly in the past without the phone having been dropped, dropping the phone could still be a cause of a quickly dying battery in this case.

Explanation:

Brianna states that her sister is mistaken about the cause of her battery dying quickly simply because it died quickly in the past because of a different cause.  However, it is possible that there are multiple causes for the same event-in this case, dropping the phone COULD have caused the event, or not, but based on the evidence given, she cannot claim that dropping it did NOT cause the event simply because the event happened for other reasons in the past.

Example Question #33 : Determining The Flaw In The Argument

Nutritionist: Consumption of too much sugar may increase the risk of diabetes and insulin resistance in many people. These people can eliminate their risk of diabetes and insulin resistance without reducing their sugar intake if they increase their consumption of whole grains such as wheat bread, because the fiber in whole grains helps reduce the negative effects of sugar on insulin response.

Which of the following best expresses a flaw in the nutritionist's reasoning?

Possible Answers:

The nutritionist assumes that fiber is the only way to counteract the negative effects of sugar.

The nutritionist fails to consider that increasing consumption of whole grains alone will not reduce the effects of sugar on the insulin response enough to eliminate the risk of diabetes and insulin reduction.

The nutritionist takes for granted that the fiber in whole grains has no negative side effects.

The nutritionist fails to recognize that reducing sugar intake can have other health benefits.

The nutritionist fails to consider that some people are allergic to whole grains.

Correct answer:

The nutritionist fails to consider that increasing consumption of whole grains alone will not reduce the effects of sugar on the insulin response enough to eliminate the risk of diabetes and insulin reduction.

Explanation:

While some of the incorrect answer choices may be true (it's reasonable to say that reducing sugar intake does have health benefits beyond reducing or eliminating risk of diabetes and insulin resistance) they do not address a flaw in the nutritionist's reasoning (that increasing whole grain consumption alone is sufficient to eliminate the risk of diabetes and insulin resistance because of fiber's ability to reduce negative effects of sugar on insulin response).  It's possible that the fiber in whole grains doesn't reduce the negative effects enough to eliminate the risk altogether.

Example Question #34 : Determining The Flaw In The Argument

Every attractive person is confident in their own skin. Mike is a smart, young professional who is confident in his own skin. He also has a beautiful, long-term girlfriend. He must also be attractive.

Which of the following best expresses the flaw in the reasoning outlined above?

Possible Answers:

Infers that the attractiveness of one's partner is indicative of one's own attractiveness.

Illicitly uses the word "attractive" in two different meanings. 

Fails to consider whether Mike is confident in his own skin.

Mistakes a condition that could be true for one that could never be true. 

Mistakes a sufficient condition for a necessary one.

Correct answer:

Mistakes a sufficient condition for a necessary one.

Explanation:

From the beginning of this passage, it is clear that it is necessary for a person to be confident in their own skin in order to be attractive. But we know nothing about whether a person who is confident in their own skin (and is a young, successful professional with a beautiful girlfriend) must also be attractive.

Example Question #35 : Flaw

Several leading experts in the field of economics have predicted that the rate of growth in Yakistan will increase of the next few years. However, one Professor from the University of Kazubistan has conclusively proven that economic predictions tend to be unreliable. Therefore, we can conclude that Yakistan will experience negative growth for the next few years.

Which one of the following best explains in the flaw in the reasoning above?

Possible Answers:

It relies on the testimony of leading experts in the field of economics who may have an incentive to overstate their findings for political reasons.

It assumes that if we cannot make accurate predictions about a situation that the opposite of the predictions is correct.

It does not specify what it means to experience negative growth.

It relies on a Professor with unspecified qualifications.

It relies on an ambiguous use of the term “growth.”

Correct answer:

It assumes that if we cannot make accurate predictions about a situation that the opposite of the predictions is correct.

Explanation:

The major flaw in the reasoning of the passage is that the stimulus in no way proves that Yakistan will experience negative growth. Simply showing that a prediction of positive growth may be inaccurate does not prove the opposite statement. Only the correct answer shows this flaw. The other answers either are irrelevant or not an actual flaw in the stimulus.

Example Question #36 : Flaw

Russell: Not all high-carbohydrate diets are unhealthy. Several conclusive studies have shown that people on high-carbohydrate diets can obtain a full complement of healthy foods.

 

Steven: You are wrong to assert that high-carbohydrate diets cannot be unhealthy. Eating a lot of carbohydrates can prevent people from consuming nutritious vegetables and fruits. Also, people whose diets are heavy in carbohydrates tend to engage in risky behavior that reduce their standards of living.

Steven’s response to Russell is most vulnerable to the criticism that his reply

Possible Answers:

Uses complex language to ignore the issue Russell is attempting to raise.

Is directed against an argument that Russell did not make.

Takes for granted that carbohydrates are unhealthy.

Relies on an ambiguous use of the term “unhealthy.”

Does not disprove the argument that risky behavior is actually associated with a healthier lifestyle

Correct answer:

Is directed against an argument that Russell did not make.

Explanation:

Steven’s response to Russell is non-responsive. Russell is only saying that it is possible to be healthy even if you have a high-carbohydrate diet. Steven only points out scenarios where one’s health is compromised by having a diet heavy in carbohydrates but does not prove that it is impossible to have a healthy diet that is heavy in carbohydrates. The correct answer points out this problem.

Example Question #33 : Determining The Flaw In The Argument

Journalist: Television programming executives are always searching for the right combination, but are essentially never successful. New shows are constantly put behind hits in vain efforts to boost new projects, while previously well-watched shows are shunted around with no purpose other than to accommodate special events like sports or election coverage.

Which of the following best describes the flaw with the journalist's argument?

Possible Answers:

Programming at television networks is typically heavily reliant on statistical models.

Network television schedules are determined by many factors other than just viewer ratings.

The position of "programming executive" is not a position of similar rank across different networks.

Most television viewers are unaware of how a television network schedules its programming.

Network television ratings are difficult to measure in small sample sizes.

Correct answer:

Network television schedules are determined by many factors other than just viewer ratings.

Explanation:

The argument is essentially a blanket castigation of "television programming executives," especially for the way they move shows with specific ratings around the schedule. This means that the journalist assumes that all programming decisions are made based on ratings alone, which the commentary about "sports or election coverage" belies.

Example Question #35 : Determining The Flaw In The Argument

Oak boards are the most common type of wood used for building houses that are intended to stand for more than one-hundred years. But recently, a large number of houses intended to stand for more than one-hundred years have only been standing for eighty-five years. A national study concluded that the type of wood boards used in many of these houses could not have been oak because no other factor in building a house would reduce a house’s life by fifteen years.

Which of the following statements best describes the flaw in the national study’s conclusion.

Possible Answers:

Pine boards do not last as long as oak boards.

Several other factors combined could have reduced the life of the house by fifteen years.

Many of these houses were recently subjected to uniquely destructive storms.

Oak boards were not as common when those houses were built because of global warming.

Fifteen years is within one standard deviation for houses with a lifespan of one-hundred years.

Correct answer:

Several other factors combined could have reduced the life of the house by fifteen years.

Explanation:

Several factors combined takes every possible reason why the houses have a reduced lifespan. The recent large storms answer is intriguing, until you realize that recent large storms could be included in the several other factors combined answer. Remember, the question asks for the BEST description of flaw in the conclusion. This means that, while storms and pine boards could have been part of the correct answer, they are not the best answer because the several factors combined answer is more inclusive.

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