LSAT Logical Reasoning : Determining which answer is an assumption on which the argument depends

Study concepts, example questions & explanations for LSAT Logical Reasoning

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Example Questions

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Example Question #1 : Necessary Assumption

Standard sheets of printer paper do not vary in the amount of wood pulp that they contain. Twenty-five percent of the wood pulp contained in a certain class of sheets of standard printer paper (Class B) was recycled from used sheets of standard printer paper of a different class (Class A). Since all Class A sheets were recycled into Class B sheets and since the amount of material other than wood pulp in a sheet of standard printer paper is negligible, it follows that Class B contains 4 times as many sheets of paper as Class A.

The conclusion of the argument follows logically if which one of the following is assumed?

Possible Answers:

When a sheet of standard printer paper is a recycled, all of its wood pulp is recovered.

The percentage of wood pulp in a sheet of standard printer paper that can be recovered during recycling varies depending on how such paper was used.

Class B sheets of paper cannot be recycled further.

All of the paper in Class A had been made from recycled wood pulp.

Unrecycled wood pulp is of better quality than recycled wood pulp.

Correct answer:

When a sheet of standard printer paper is a recycled, all of its wood pulp is recovered.

Explanation:

Since 25 percent of wood pulp in the Class B sheets comes from recycled Class A sheets, the maximum number of Class B sheets is 4 times the number of Class A sheets. However, the correct answer correctly notices that the maximum number of Class B sheets can be produced only if all pulp from the Class A sheets can be recovered through recycling; if less than all of the pulp can be recovered, the actual number of Class B sheets produced will fall short of the maximum. For example, if there were 100 Class A sheets recycled, but only 25 percent of pulp could be recovered through recycling, only 100 Class B sheets could be produced.

Example Question #1 : Necessary Assumption

Soccer players are faster than baseball players because soccer players use more strenuous training programs. Baseball players should use the same training programs as soccer players to become more athletic. More athletic players will be more successful.

Which of the following, if assumed, would allow the conclusion above to be properly drawn?

Possible Answers:

Players who become faster become more athletic

Baseball players do not train very often during the season

Fast baseball players sometimes also play soccer

Baseball requires different skills than soccer

Speed is important to success in baseball

Correct answer:

Players who become faster become more athletic

Explanation:

The argument asserts that different training programs cause soccer players to be faster than baseball players.  The next assertion is that baseball players would become more athletic if they used training programs of soccer players.  This only follows if becoming faster necessarily makes one more athletic.

Example Question #1 : Determining Which Answer Is An Assumption On Which The Argument Depends

It is important that each driver have an insurance policy before driving on the road. Otherwise, people may not be compensated when they are injured in car accidents. Everyone injured in accidents deserves to be compensated.

The argument assumes which of the following?

Possible Answers:

Those who are injured in accidents are never at fault for those accidents

If every driver is insured, every person injured in an accident will be compensated

Compensation always requires monetary payment

No one who is in an accident but is uninjured deserves to be compensated

All car accidents result in injuries

Correct answer:

If every driver is insured, every person injured in an accident will be compensated

Explanation:

If injured people might not be compensated even if every driver has insurance, then the argument's conclusion does not follow.

Example Question #2 : Determining Which Answer Is An Assumption On Which The Argument Depends

The production of pencil sharpeners can no longer be profitable. This is because various factors have decreased demand for pencil sharpeners. First, pens are used far more than they once were. Second, those who use pencils often use mechanical pencils. Finally, increased use of electronics has decreased the need for handwriting.
The argument depends on which of the following assumptions?
Possible Answers:
Production of pencil sharpeners cannot be profitable if there is a decreased demand for them
Pencil sharpeners are only in demand for the purpose of sharpening pencils
Students no longer prefer pencils over pens for math calculations
Anything that can be accomplished with pencils can also be accomplished with electronics
Availability of mechanical pencils has increased
Correct answer: Production of pencil sharpeners cannot be profitable if there is a decreased demand for them
Explanation: The argument's assertion is that production of pencil sharpeners cannot be profitable. The argument does not link this assertion to the rest of the argument, however. Instead, it supports the claim that demand has decreased. The argument assumes that decreased demand has made production of pencil sharpeners unprofitable.

Example Question #3 : Necessary Assumption

The business model of internet cafes is no longer capable of success in the United States. This is because the availability of internet has skyrocketed over the past several years. Free wifi is offered in most major coffee shops and stores. Additionally, Americans have mobile devices with plans that provide them with internet access. For those without devices, public libraries also provide computers offering internet access, free of charge.  

The argument depends on which of the following assumptions?

Possible Answers:

Public libraries are the only accessible locations where anyone can use the internet. 

Internet cafes can still be profitable in other countries, just not the United States. 

Major coffee shops are in direct competition with internet cafes. 

Internet cafes do not offer any other services, aside from online access, that would enable them to be profitable. 

Internet cafes were profitable five years ago. 

Correct answer:

Internet cafes do not offer any other services, aside from online access, that would enable them to be profitable. 

Explanation:

The correct answer is:

Internet cafes do not offer any other services, aside from online access, that would enable them to be profitable. 

The crux of the argument is that internet cafes are not successful because the service that they offer -- online access -- is now made available for free by other outlets. However, this argument depends on the assumption that internet cafes do NOT offer any other services that would make them profitable -- such as a community base that would attract clients, or food and beverages that consumers would be interested in buying. 

Example Question #4 : Necessary Assumption

A law degree is necessary to practice as an attorney. Further, no one who has demonstrated moral turpitude may be admitted to practice law. Consequently, Smith, who was convicted of embezzlement several years ago, cannot be admitted to practice law. 

The argument follows logically if which of the following is assumed?

Possible Answers:

Behavior that demonstrates moral turpitude includes the commission of certain crimes. 

Smith's conviction is nor revocable. 

Embezzlement raises issues of integrity which can bar someone from practicing as an attorney. 

Embezzlement demonstrates moral turpitude. 

Embezzlement is a serious crime. 

Correct answer:

Embezzlement demonstrates moral turpitude. 

Explanation:

To answer this question, it is necessary to realize that the criteria to practice law requires that a person not demonstrate moral turpitude. Therefore, there has to be a link between Smith's embezzlement and the moral turpitude. Therefore, if embezzlement demonstrates moral turpitude, then the argument flows logically. 

Example Question #1 : Necessary Assumption

Sports commentator:  Miles has received criticism from fans and sportswriters as a second-rate basketball player because he is considered too short and he cannot dribble effectively with his left hand. But this evaluation of Miles’s virtues as a basketball player is unfair, since there have been successful running backs in professional football who are short and who exhibited a strong preference for veering towards the right to evade tacklers.

Which one of the following is an assumption on which the argument depends?

Possible Answers:

It is unfair to jump to conclusions about athletic prowess and effectiveness simply because a player is short.

Evaluation of basketball players must take into account what position they play on a team, and in particular, what kind of role a coach assigns to them to effectuate the goals of the team.

Miles’s virtues as a basketball player should be determined by relevant statistics, such as shooting percentage and steals.

Some sports fans do not appreciate how short stature can be advantageous in football and basketball and how quickness can override any handicap arising from preferring the right over the left when moving on a court or field.

Height and left-right preferences have comparable value in football and basketball.

Correct answer:

Height and left-right preferences have comparable value in football and basketball.

Explanation:

In any assumption question, we must identify what term, concept, or idea is expressed in the evidence that does not appear in the conclusion. In this instance, the evidence concerns football running backs. Therefore, any viable answer choice must refer meaningfully to football. Any answer choice that does not do this should be eliminated. The essence of the argument here involves an assumption that football and basketball are comparable sports. So the correct answer is: Height and left-right preferences have a comparable value in football and basketball.

Example Question #2 : Determining Which Answer Is An Assumption On Which The Argument Depends

It is wrong to condemn the eating of lobster. Lobsters do not have the kind of cognitive abilities that permits meaningful self-awareness, and that sort of cognitive ability is essential to experience suffering.

The conclusion above follows logically if which one of the following is assumed?

Possible Answers:

Any sentient beings that can experience suffering deserve to be treated respectfully.

If lobsters ought not to be eaten because they can experience suffering, then the same is true with respect to pigs.

Only organisms that are self-aware can experience suffering.

Only sentient beings that can experience suffering ought to be considered outside the realm of edible food for humans.

Any sentient being that can experience suffering must necessarily have highly developed cognitive abilities.

Correct answer:

Only sentient beings that can experience suffering ought to be considered outside the realm of edible food for humans.

Explanation:

The assumption must speak to the issue of “experiencing suffering,” since that is the missing term in the conclusion. The correct answer links that new term to the conclusion regarding what humans ought to eat and not eat. Thus, the correct answer is: Only sentient beings that can experience suffering ought to be considered outside the realm of edible food for humans.

Example Question #3 : Determining Which Answer Is An Assumption On Which The Argument Depends

Outlining a story's plotline before actually drafting the story reduces the amount of writing time.  But writing a story through free-writing to generate a first draft, which then can be reformulated through rigorous editing, produces a more creative narration of events.  Therefore, when quality fiction writing is more important than generating a quick writing product, outlining should give way to free-writing.

Which one of the following is an assumption required by the argument?

Possible Answers:

The more creative the storytelling, the better the finished product, at least when it comes to fiction.

Fiction writing is a painstaking process that cannot be made easier through outlining.

Writing is never improved through outlining or other time-saving strategies.

Creative narration of events in a story enhances the quality of fiction writing.

Free-writing is best used in fiction writing, but its value in expository writing is suspect.

Correct answer:

Creative narration of events in a story enhances the quality of fiction writing.

Explanation:

The conclusion speaks of free-writing as better than outlining when it comes to generating quality fiction.  The premise (i.e., the evidence) for that conclusion speaks of "creative narration of events."  That idea does not appear in the conclusion, so in order to link the premise to the conclusion, the assumption must address it in some meaningful way.  The correct answer here does just that, by linking the idea of "creative narration of events" and the point in the conclusion about quality fiction.

Example Question #8 : Necessary Assumption

Among the varous models of racing cars used in top-level racing competitions, one cannot predict a car's ability to reach maximum speed simply by the horsepower of the motor.  The efficiency of a motor's fuel-injection system varies significantly, even between racing cars with motors of comparable horsepower.

The argument's conclusion is properly drawn if which one of the following is assumed?

Possible Answers:

It is not possible to assess how quickly a race car can reach maximum speed without knowing how powerful is its motor.

It is possible to infer the power of a car's motor by examining the efficiency of its fuel-injection system.

For each race car, the efficiency of its fuel-injection system has a significant impact on how quickly it can reach maximum speed.

For any two race cars with comparable fuel-injection systems, the one with the more powerful motor will reach maximum speed more quickly.

All cars that reach maximum speed within six seconds have comparable motors in terms of their horsepower.

Correct answer:

For each race car, the efficiency of its fuel-injection system has a significant impact on how quickly it can reach maximum speed.

Explanation:

The conclusion of this argument speaks to the ability to predict a race car's quickness in reaching maximum speed---horsepower alone won't permit an accurate prediction.  Why?  The argument states that the efficiency of the fuel-injection system varies among comparable cars.  This suggests that the fuel-injection system is a critical factor in a car's ability to reach maximum speed.  And that indeed is the unstated assumption.  The "efficiency of the fuel-injection system" is the key term in the evidence portion of the argument that is not stated in the conclusion, and it is that key term that must be contained in the assumption.  Any answer choice that does not mention that key term can be immediately eliminated.

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