LSAT Logical Reasoning : Determining which answer must be true based on the information given

Study concepts, example questions & explanations for LSAT Logical Reasoning

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Example Questions

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Example Question #1 : Must Be True

Most successful professional football players began playing football as youths, though a significant number learned the sport later in life. No professional football player who ignored the advice of his coaches, however, has ever become successful.

If the above statements are true, which of the following must also be true?

Possible Answers:

The more attentive a professional football player is to his coaches' advice, the more likely he is to be successful.

Not all professional football players who played the sport as youths ignored the advice of coaches.

The most successful professional football players played the sport as youths.

No professional football player who learned the sport later in lafe will ignore his coaches' advice.

All unsuccessful professional football players have ignored the advice of coaches.

Correct answer:

Not all professional football players who played the sport as youths ignored the advice of coaches.

Explanation:

According to the second sentence of the passage, a necessary condition for being a successful professional football player is not ignoring the advice of coaches. So all of the successful professional football players mentioned in the passage's first sentence, including those who played the sport as youths, do not ignore the advice of coaches. That’ s what the correct answer states.

Example Question #1 : Determining Which Answer Must Be True Based On The Information Given

A growing world population has caused growing concerns about increasing famine.  The population in 2000 was 6 billion.  Ten years later the population was 7 billion.  There were also more people affected by famines in 2010 than in 2000.  Furthermore, in each year from 2000 to 2010, when the world's population increased, so did the number of those affected by famine.

Based on the information given, which of the following is true?

Possible Answers:

From 2000 to 2010, when the world's population increased, the percentage of the population affected by famine also increased

There was greater concern about famine in 2010 than in 2000

If the population increased in 2005, then more people were affected by famine in 2005 than in 2004

The population increased in every year between 2000 to 2010

If the population decreased in a particular year between 2000 and 2010, the number of those affected by famine also decreased in that year

Correct answer:

If the population increased in 2005, then more people were affected by famine in 2005 than in 2004

Explanation:

The number affected by famine always increases with the population.  Therefore, if the population increased in 2005, then the number of those affected by famine also increased.  If there was an increase in 2005, there must have been more people affected in that year than the previous year of 2004.  The available information does not allow us to draw any of the other inferences.  The number of those affected by famine could increase without a corresponding percentage of the population increase.  Neither can we draw inferences about any particular year between 2000 and 2010.

Example Question #2 : Determining Which Answer Must Be True Based On The Information Given

Most movie critics dislike Hollywood blockbusters. If someone dislikes Hollywood blockbusters they are a snob. Most people who are over the age of fifty dislike Hollywood blockbusters. Some people who dislike Hollywood blockbusters are huge fans of theater. If someone does not dislike Hollywood blockbusters they like large explosions.

Each of the following must be true EXCEPT:

Possible Answers:

Most people over the age of fifty are snobs.

If someone is not a snob, they like large explosions.

Most movie critics are snobs.

Some people who dislike Hollywood blockbusters are over the age of fifty.

Some movie critics are huge fans of theater.

Correct answer:

Some movie critics are huge fans of theater.

Explanation:

We cannot assume that some movie critics are huge fans of theater because the only connection between both is two "some" statements. The rest of the answers must be true based on inferences we can make from the stimulus.

Example Question #3 : Determining Which Answer Must Be True Based On The Information Given

The number of yoga studios in urban areas has been growing at a rapid pace. Major distributors of yoga apparel have been reaping the benefits: there has been a 25% increase in sales for yoga retail from 2007 to 2014. In a recent study, 90% of consumers who bought yoga gear reported attending yoga classes at least twice a month. 

Based on the information, which of the following is true?

Possible Answers:

There is a correlation between the increase in yoga studios and the increased sales of yoga apparel. 

There has been a 25% increase in the number of yoga studios in urban centers. 

There was not an increase in the sale of yoga apparel before 2007. 

The most yoga apparel is sold in urban centers. 

People who attend yoga classes are more likely to buy yoga apparel. 

Correct answer:

There is a correlation between the increase in yoga studios and the increased sales of yoga apparel. 

Explanation:

The correct answer is:

There is a correlation between the increase in yoga studios and the increased sales of yoga apparel. 

Given that the study indicated that 90% of yoga apparel consumers also attend yoga classes, there is in fact a correlation between the increase in yoga studios and the increase in the sale of yoga apparel. 

Example Question #4 : Determining Which Answer Must Be True Based On The Information Given

As a society, we have no excuse for the prevalence of chronic dehydration. The remedy is simply too obvious and accessible. Those who suffer from the condition seek doctors’ opinions and medications, suffer from unexplained dizziness and other symptoms, and are susceptible to sickness. To solve these problems and to increase energy and focus, these people need only to drink more water—either by itself or as a primary ingredient in other beverages.

The information above provides the most support for which of the following statements?

Possible Answers:

Doctors do not advise chronically dehydrated patients to drink more water even though that would be the best remedy

One can obtain all the health benefits of water by consuming it either by itself or as a primary ingredient in another beverage

Those who suffer from dizziness can adequately address the problem by drinking more water

Most people in the society at issue suffer from chronic dehydration

Those who suffer from chronic dehydration could increase their energy and focus by drinking more water

Correct answer:

Those who suffer from chronic dehydration could increase their energy and focus by drinking more water

Explanation:

The passage does not speak generally to the health benefits of water, the number of people affected by dehydration, or the impacts of dehydration. We can draw some conclusions, however, about the effects of drinking more water for those who are chronically dehydrated. Those who are chronically dehydrated will increase energy and focus by drinking more water.

Example Question #4 : Must Be True

Some of the college athletes playing football are also playing rugby, but none of them are playing soccer. Yet some of the soccer players are also playing rugby. For this reason, many coaches refer to rugby as the catch-all sport.

Which one of the following statements follows logically from the statements above?

Possible Answers:

There are some rugby players who play soccer but not football.

Most football players play only football and no other sport.

There are some rugby players who play neither soccer nor football.

Most rugby players also play either soccer or football.

Some of the soccer players playing rugby also play football.

Correct answer:

There are some rugby players who play soccer but not football.

Explanation:

Only three assertions are made in the paragraph: 1) no players play both football and soccer; 2) some players play both football and rugby; 3) some players play both soccer and rugby. There must be, therefore, a subset of players who play both soccer and rugby but not football.

Example Question #5 : Must Be True

Many of Franz Liszt’s piano compositions are in fact transcriptions of works originally written by other composers. Liszt often performed these transcriptions in his own widely-attended concerts. Because orchestral works were not as widely performed in the 19th century as they are today, Liszt’s transcriptions helped to popularize many of these works, such as Beethoven’s symphonies. The transcriptions themselves were uniformly both challenging and masterful. Some listeners even preferred the piano transcriptions to the original works.

Which one of the following statements is most strongly supported by the information above?

Possible Answers:

Most of the orchestral compositions transcribed by Liszt are more popular today than they were in the 19th century.

At least some of Liszt’s transcriptions of orchestral works are more popular than Liszt’s original compositions.

At least some popular orchestral works have been transcribed into challenging piano compositions by Liszt.

Liszt’s own concerts, on average, were more widely attended than most orchestral concerts.

The most masterful and challenging of Liszt’s compositions were transcriptions of orchestral works by other composers.

Correct answer:

At least some popular orchestral works have been transcribed into challenging piano compositions by Liszt.

Explanation:

The correct answer choice is the only one that does not indulge in comparative analysis. We know that Liszt transcribed orchestral works, that many of these works became popular as a result, and that the transcriptions were challenging (and masterful). The incorrect answer choices all attempt, by the use of “more” or “most,” to compare popularity or other factors. Such comparisons go beyond the information provided in the passage.

Example Question #8 : Must Be True

If the bookstore does not respond to modern trends, it will not stay in business. And if the bookstore does not offer electronic books in a popular format, it will not respond to modern trends. Furthermore, no electronic book format is popular unless it can be used on each of the top three e-book readers.

If the statements above are true, which one of the following must be true?

Possible Answers:

It is significantly more likely that the bookstore will stay in business if it responds to modern trends than if it does not respond to them.

If the bookstore stays in business, it will offer electronic books in a format which can be used on the top three e-book readers.

Popular electronic book formats generate more business for the bookstore than unpopular formats.

If the bookstore offers electronic books in a format which can be used on each of the top three e-book readers, it will stay in business.

The bookstore will probably stay in business if it offers electronic books in a popular format.

Correct answer:

If the bookstore stays in business, it will offer electronic books in a format which can be used on the top three e-book readers.

Explanation:

The correct answer choice correctly notes that the bookstore will not stay in business unless it offers electronic books in a popular format as defined. Therefore, if the bookstore does stay in business, it must offer electronic books in such a format. The other answer choices employ incorrect information and/or probability reasoning unsupported by the argument. Remember: we do not know the conditions under which the bookstore will stay in business; we only know for certain what will cause the bookstore to not stay in business.

Example Question #5 : Determining Which Answer Must Be True Based On The Information Given

It appears that warm temperatures tend to improve both productivity and attitudes. Empirical evidence supports the general assumption that outdoor temperatures affect the way people feel and, perhaps as a result, the amount they get done. These conclusions are drawn from a recent study which found that when temperatures increase at the beginning of spring people are more likely to smile, make more money than in the winter, greet strangers, and report that they are content with their lives.

Which of the following is most supported by the study?

Possible Answers:

Warm temperatures increase happiness and earnings

Those who smile often are likely to make more money than those who do not

People are more likely to smile at the beginning of spring than at other times

When it is 80 degrees outside, people are more likely to smile than when it is 30 degrees

Those who greet strangers are likely to make more money and smile more often than those who do not

Correct answer:

People are more likely to smile at the beginning of spring than at other times

Explanation:

The study cited by the author does not directly support the author's conclusion.  Instead, the study describes a few specific facts observed only at the beginning of the spring.  The study supports the claim that people smile more often at the beginning of the spring than at other times, but it does not support broader claims about temperatures or seasons.

Example Question #6 : Must Be True

Light bulb manufacturers have recently been forced to recall certain models of their LED bulbs due to overheating.  The bulbs reportedly heated to the point that they produced smoke and fire, damaging customers’ lamps, walls, carpets, and other furniture.  But many of these accidents could have been avoided had customers merely practiced energy conservation and turned off the lights when not in use.  Indeed, according to one consumer study, over 90% of property damage from light bulb overheating occurs when no one is in the room to see what is happening.

The statements above, if true, most strongly support which one of the following?

Possible Answers:

Some property damage from light bulb overheating would likely not have occurred if more customers turned off their LED light bulbs when not in use.

A light bulb is less likely to produce smoke and fire if a person is in the room during the period of time when it overheats.

When a customer’s lamp, wall, carpet, or other furniture has been damaged by an overheated light bulb, it is probable that the customer has not been practicing energy conservation.

LED light bulbs are, according to customers, less safe than other types of light bulbs.

If more customers had turned off their LED light bulbs when not in use, a recall of LED light bulbs would not have been necessary.

Correct answer:

Some property damage from light bulb overheating would likely not have occurred if more customers turned off their LED light bulbs when not in use.

Explanation:

The correct answer choice is basically a restatement of the second and third sentences of the passage.  It is the only answer choice that does not make assumptions based on information not specifically given in the passage.  It is unclear from the passage whether the recall could have been avoided or whether LED light bulbs generally are less safe than other light bulbs.  Further, no clear conclusions can be drawn from the passage regarding the likelihood of an individual light bulb producing smoke and fire, or whether a customer has been practicing energy conservation.

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