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

Example Question #21 : Necessary Assumption

Nutritionist: Water is often called the “universal elixir” because of its importance to the body in recovering from illnesses as well as maintaining general good health.  But water, in and of itself, has little nutritional value.  Furthermore, we often have a difficult time getting young people to consume water; they tend to prefer soda or juice because of water’s bland taste.  Indeed, over 60% of the liquids consumed on high school campuses are found in soda machines.  The solution is found in mineral waters, which contain all the benefits of water, plus nutrients and a distinct taste.  Nutrition among our youth would significantly improve if we replaced soda machines in schools with machines containing various types of mineral water.  

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

Possible Answers:

Most of the liquids consumed on high school campuses, other than those found in soda machines, are liquids other than water.

The nutrients in mineral waters provide a significant source of nutrition comparable to the nutrition found in various foods.

Mineral waters taste as good as or better than most types of soda.

Most high school students are not allowed to bring drinks onto campus that they obtained outside of campus.

A significant portion of students who consume liquids from soda machines would, in their absence, consume liquids from mineral water machines.

Correct answer:

A significant portion of students who consume liquids from soda machines would, in their absence, consume liquids from mineral water machines.

Explanation:

Providing students access to healthier liquids would not improve nutrition among students if the students didn’t actually drink the liquids.  Therefore, the argument assumes that at least some portion of students (enough to be significant) would replace their normal soda drinking with mineral water drinking.  The other answer choices, while they may be relevant, are not required for the argument to be sound.

Example Question #271 : Lsat Logical Reasoning

City officials care a great deal about maintaining man-made structures so as to avoid liability.  For instance, officials act quickly when bridges deteriorate to the point of causing concrete to fall on roadways.  There can be no doubt that the officials' only concern is liability, because they rarely respond with similar urgency to address branches falling from rotting trees. 

Which of the following assumptions is necessary for the conclusion to be properly drawn?

Possible Answers:

City officials are liable for harm from man-made structures that are not maintained but not for branches falling from rotting trees

Deteriorating bridges are one of the most common types of roadway hazards

Bridges are not the only type of man-made structure that requires maintenance

Branches fall from rotting trees as frequently as concrete falls from deteriorating bridges

City officials only act quickly to address deteriorating bridges when concrete begins falling on roadways

Correct answer:

City officials are liable for harm from man-made structures that are not maintained but not for branches falling from rotting trees

Explanation:

The argument seeks to prove that city officials maintain man-made structures only to avoid liability.  The conclusion does not follow, though, if officials do not maintain rotting trees even though rotting trees also lead to liability.

Example Question #272 : Lsat Logical Reasoning

Student: Obtaining student loans will be more beneficial to my future than working full-time while in school.  If I obtain student loans for my remaining years in college, I will be in significant debt after I graduate from college.  If I do not obtain student loans, and instead secure a full-time job while in school, I will avoid such debt.  However, I cannot obtain a job in my chosen field after graduation without good grades, and my grades will suffer greatly if I am working full-time while attending school.  

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

Possible Answers:

The amount of debt incurred by the student as a result of student loans will be lower than the amount of net income attained by working full-time while in school.

A full-time job obtained during school will not pay a higher salary than a job obtained after graduation.

Avoidance of significant debt is the most important factor in determining what is beneficial to the student’s future.

Obtaining a job in the student’s chosen field after graduation is more beneficial to the student’s future than avoiding significant debt.

Employers in the student’s chosen field consider only good grades when deciding whether to hire new graduates.

Correct answer:

Obtaining a job in the student’s chosen field after graduation is more beneficial to the student’s future than avoiding significant debt.

Explanation:

The conclusion of the argument, found in the first sentence, is that obtaining student loans will be more beneficial to the student’s future than working-full time while in college.  For this conclusion to follow, it must be the case that the consequences of obtaining such loans (significant debt) are less costly – i.e. more beneficial – than the consequences of working full-time while in school (a drop in grades).  The remaining answer choices that are either not helpful to the argument, or are helpful to the argument but not required for the conclusion to logically follow.

Example Question #21 : Determining Which Answer Is An Assumption On Which The Argument Depends

The campaign for increased care of the environment is doomed to fail.  At this point, nothing can be done to prevent the melting of polar ice caps.  The melting would continue even if all conduct harmful to the environment ended today.  It is simply too late to stop the inevitable melting.

Which of the following must be assumed in order for the conclusion to be properly drawn?

Possible Answers:

The campaign for increased care of the environment will fail unless it prevents the melting of ice caps

Melting of ice caps is caused by a failure to care for the environment

The campaign for increased care of the environment will not decrease conduct harmful to the environment

Melting of ice caps will cause harm to the environment

The campaign for increased care of the environment will not cause people to care for the environment

Correct answer:

The campaign for increased care of the environment will fail unless it prevents the melting of ice caps

Explanation:

The passage asserts that the campaign for increased care of the environment is doomed to fail.  The passage demonstrates, however, only that ice caps will melt despite the campaign.  The argument's conclusion is only properly drawn if melting ice caps necessarily means that the campaign has failed.

Example Question #274 : Lsat Logical Reasoning

Defense attorney: At this point it is abundantly clear that the rich receive better representation in the legal system.  Those who can afford private attorneys often spend thousands or even millions of dollars on legal fees.  This allows the private attorney to focus exclusively on that client's case, devoting his or her time and resources to it.  Meanwhile, the poor are forced to either represent themselves or rely upon an appointed public attorney, who has hundreds of cases that must be handled simultaneously.

Which one of the following is an assumption required by the defense attorney's argument?

Possible Answers:

If a public attorney is appointed to a particular case, that attorney spends no more time or resources in his or her representation on that case than on the other cases which are being handled simultaneously.

Those attorneys who can focus exclusively on a client's case provide better representation than either those who represent themselves or attorneys who have many cases that must be handled simultaneously.

Private attorneys never give discounts on legal fees to those who cannot afford their higher rates.

Those who represent themselves do not have legal training equal to that of attorneys who have attended law school and passed the bar exam.

The more money one spends on legal fees, the more competent one's attorney will be in handling a particular case.

Correct answer:

Those attorneys who can focus exclusively on a client's case provide better representation than either those who represent themselves or attorneys who have many cases that must be handled simultaneously.

Explanation:

The underlying assumptions in the argument are that 1) attorneys who focus exclusively on one case have the time and resources to give better representation than those who don't  have such resources; 2) those attorneys also provide better representation than those who represent themselves.  The remaining answer choices include assumptions that the defense attorney may be making, but they are not required for the argument to be valid.

Example Question #275 : Lsat Logical Reasoning

At a particular bakery, sales have increased in each of the last six months. The top-selling item at the bakery is the peanut butter cookie. Due to concerns over nut allergies, the bakery has temporarily taken the peanut butter cookie off the menu and replaced it with the all-new snickerdoodle cookie. It is fair to say that the bakery's sales will not increase for a seventh consecutive month.

Which of the following assumptions does the author's argument rely upon?

Possible Answers:

The peanut butter cookie was so significant to overall sales that its replacement will halt sales growth.

Aside from the peanut butter cookie, the rest of the menu at the bakery remains unchanged.

The snickerdoodle cookie will not be the top-selling cookie.

The snickerdoodle cookie will not be as popular as the peanut butter cookie was.

The bakery has been in business for only six months.

Correct answer:

The peanut butter cookie was so significant to overall sales that its replacement will halt sales growth.

Explanation:

Regardless of how popular the snickerdoodle cookie turns out to be, the author's argument relies on the assumption that the sale of the peanut butter cookie was so significant to overall sales that its replacement will cause the bakery's overall sales not to increase during the seventh month. Even if the snickerdoodle cookie is as popular as the peanut butter cookie, sales could stop growing for other reasons.

Example Question #271 : Lsat Logical Reasoning

Every winter, a species of North American bird flies south. Every year, the migration begins during the first week of November. For the last fifty years, if the average temperature is less than 40 degrees Fahrenheit during the final week of October, the birds fly southwest. If the average temperature during that time is more than 40 degrees Fahrenheit, the birds fly southeast.  his year, the average temperature during the final week of October is going to be 45 degrees Fahrenheit. Therefore, the birds will fly in the southeast direction.

Which most correctly describes the necessary assumption(s) that the author makes?

Possible Answers:

All of the above

The author assumes that the birds will continue to travel during the winter.

The author assumes the forecast for the final week of October will be correct.

The author assumes there is a causal relationship between the average temperature in the final week of October and the direction in which the birds fly.

The author assumes that the birds are familiar with what day it is.

Correct answer:

The author assumes there is a causal relationship between the average temperature in the final week of October and the direction in which the birds fly.

Explanation:

In concluding that the birds will fly southeast, the author assumes there is a causal relationship between the average temperature in the final week of October and the direction in which the birds fly, and that the correlation is not merely coincidental. If the correlation is coincidental, then it will not matter whether the forecast is correct or not.

Example Question #277 : Lsat Logical Reasoning

Politician: Building up the military is a necessary part of keeping the nation safe. Other nations will invade our territory if they sense weakness, and having a strong national defense will make other nations think twice before they threaten our borders. Only an impressive military will allow us to make the world safe.

Which of the following is a necessary assumption in the argument made above?

Possible Answers:

The nation's military should always be as strong as the government can possibly make it.

The proper size of the nation's military is a divisive political argument.

The nation's military is not currently strong enough to invade other nations.

The way to show military strength is to invade other nations with weaker militaries.

A nation will always invade another nation that it views as weak militarily.

Correct answer:

A nation will always invade another nation that it views as weak militarily.

Explanation:

The politican states that the nation must have a strong military to prevent other nations from invading the country's borders. This line of thinking necessarily relies on the assumption that other nations will invade any country whose military is viewed as too weak. If other nations do not think in this manner, then the politican's argument completely falls apart.

Example Question #278 : Lsat Logical Reasoning

Scientist: Much of the marine life has been dying along the coastline for decades. The introduction of foreign fish began thirty years ago, with a small aquaculture development in the southern part of the region. Returning the marine environment to the way it was a century ago will allow a more diverse amount of species to flourish in these waters.

Which of the following is a necessary assumption of the scientist’s argument?

Possible Answers:

Foreign fish species are easily eradicated from the coastline’s marine environment.

Native fish species are far superior to the foreign fish species found in this particular coastline.

The foreign fish species have been harming a number of native, local marine species.

The native fish species should have been able to handle the foreign fish species much better.

The introduction of foreign fish was done to intentionally harm local fish species.

Correct answer:

The foreign fish species have been harming a number of native, local marine species.

Explanation:

The passage's main argument is that eliminating the foreign fish species will allow native fish species to flourish in a manner that they used to be able to before the foreign fish were introduced. The assumption that the foreign fish are actually hurting the native fish is necessary for the passage's argument to make logical sense.

Example Question #279 : Lsat Logical Reasoning

Each year, fewer students study the humanities. While there might still be interest in the subjects of literature, art history, and philosophy, the financial rewards of studying business, science, and engineering have proven too enticing for most students.

Which of the following is a necessary assumption of the passage?

Possible Answers:

Students choose college majors with little regard for post-college plans.

Students prefer the intellectual pursuits of business, science, and engineering.

Students do not make the best career choices when choosing college majors.

Students are most likely to choose the major with the most lucrative career path.

Students find literature, art history, and philosophy boring as subjects of inquiry.

Correct answer:

Students are most likely to choose the major with the most lucrative career path.

Explanation:

The passage rather snidely notes that the majors that are most popular are not chosen based on what students actually wish to study. For this argument to work, students must be choosing their college studies entirely based on financial rewards and benefits in their post-college career.

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