LSAT Logical Reasoning : Determining which answer cannot be true based on the information given

Study concepts, example questions & explanations for LSAT Logical Reasoning

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Example Questions

Example Question #1 : Determining Which Answer Cannot Be True Based On The Information Given

Two things are true of all good deeds. First, they are accompanied by feelings of satisfaction. Second, if they are publicly known, they elicit general approval.

If all of the above statements are true, then which of the following cannot also be true?

Possible Answers:

Good deeds are good solely because they are accompanied by feelings of satisfaction.

Even if they frequently elicit general approval when known publicly, some deeds that are accompanied by feelings of satisfaction are not good deeds.

Some good deeds that are not publicly known are not accompanied by feelings of satisfaction.

Some publicly known deeds that elicit general approval are not accompanied by feelings of satisfaction.

Every publicly known act that is accompanied by feelings of satisfaction is a good deed.

Correct answer:

Some good deeds that are not publicly known are not accompanied by feelings of satisfaction.

Explanation:

According to sentences 1 and 2 of the passage, all good deeds are accompanied by feelings of satisfaction. Therefore the correct answer has to be false. That is, no good deed, whether or not publicly known, comes without satisfaction.

Example Question #2 : Determining Which Answer Cannot Be True Based On The Information Given

The price of a barrel of crude oil fell by 15 percent over the last month. Economists point to several causes, including the discovery of new reserves of oil, the increased accessibility of alternative sources of fuel, the growth of mass transit, the decline of car sales, and the increase in non-fuel-consuming means of transportation, such as bicycles, over the same time frame.

Which of the following does the above argument NOT imply?

Possible Answers:

The discovery of new reserves of oil has increased the supply, created a surplus, and thus driven the price of oil down.

People are more likely to purchase new cars if the price of oil is low.

The increased accessibility of alternative sources of fuel has reduced the demand for oil and thus driven the price of a barrel of crude oil down.

If they have access to both, some people would rather use alternative sources of fuel instead of oil.

The growth of mass transit systems, which transport more people and use less fuel, has reduced demand for oil and driven the price of oil down.

Correct answer:

People are more likely to purchase new cars if the price of oil is low.

Explanation:

The argument can be said to imply all of the choices except that people are more likely to purchase new cars if the price of oil is low. In fact, the argument implies the opposite. There has been a decline in car sales over the last month, while the price of oil has gone down 15 percent. If there is any relationship between the two, it is not that low oil prices equates to more new car purchases. The argument implies, rather, that the decline of car sales contributed to the fall in the price of oil.

Example Question #3 : Determining Which Answer Cannot Be True Based On The Information Given

Fewer people go without email with each passing year. Not only are younger and younger children signing up for their own accounts, but the generation that was largely too old and out of touch to have ever had an account is slowly dying. It is entirely likely that no one over the age of 10 will be without an email account within the next ten years.

Which of the following statements cannot be true based on the above statement?

Possible Answers:

Email is a pervasive form of communication that is used by many different people.

Older generations are much more likely than younger ones to adopt new forms of communication.

Older generations find email to be an awkward form of communication compared to letters and the telephone.

Many younger people use many more communication methods than strictly email.

Email is used differently by specific age groups, leading to a diverse pattern of email usage.

Correct answer:

Older generations are much more likely than younger ones to adopt new forms of communication.

Explanation:

The statement explicitly states that one of the reasons email will be essentially universal is that the older generation, which had never used email, would be dying out. This indicates that younger generations, which are only growing, are much more likely to adopt brand new forms of communication.

Example Question #4 : Determining Which Answer Cannot Be True Based On The Information Given

Many home renters buy their first homes believing that it is clearly more profitable to make mortgage payments than to pay rent. Other costs, such as maintenance, property taxes, and insurance must be factored in, however. All housing expenses together total at least 40% of most homeowners' income.  It is not financially reasonable to spend any more than 30% of income on housing expenses.

If the information is correct, which of the following cannot be true?

Possible Answers:

A majority of renters pay an unreasonable amount for housing expenses

A majority of homeowners have unreasonable housing expenses

A minority of homeowners have unreasonable housing expenses

A minority of homeowners have reasonable housing expenses

The combination of property taxes, insurance, and home maintenance costs is greater than mortgage payments for a minority of homeowners

Correct answer:

A minority of homeowners have unreasonable housing expenses

Explanation:

We know from the information given that most homeowners have housing expenses that are at least 40% of their incomes. If housing expenses of more than 30% of a homeowner's income is unreasonable, then at least a majority of homeowners have unreasonable housing expenses.

Example Question #5 : Determining Which Answer Cannot Be True Based On The Information Given

Most dogs have four legs. Some animals with four legs make great companions. Some dogs are fluffy.

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

Possible Answers:

If a dog has four legs then it will be a great companion.

Some great companions are fluffy.

Some dogs that are fluffy have four legs.

Some animals with four legs are dogs.

Most animals with four legs make great companions.

Correct answer:

Some animals with four legs are dogs.

Explanation:

The correct answer comes from the stimulus alone. The correct answer is the only one that must be true.

Example Question #6 : Determining Which Answer Cannot Be True Based On The Information Given

Most four-legged, domesticated animals are dogs. All dogs are pets. No pets are allowed inside of the school building. All domesticated animals on school property must be leashed. All domesticated animals are pets. 

Which of the following cannot be true?

Possible Answers:

A domesticated animal that is not a dog is leashed on school property.

A four-legged, non-domesticated animal is allowed inside of the school property. 

A dog is permitted near school property.

A domesticated animal that is not a dog is permitted inside the school building.

A four-legged animal is not leashed on school property. 

Correct answer:

A domesticated animal that is not a dog is permitted inside the school building.

Explanation:

The difficult in this questions lies simply in the complicated structure of the passage and the confusing phrasing of the possible answers. In the end, however, the answer is quite simple. No domesticated animals (dogs or otherwise) are allowed inside the school building, because all domesticated animals are pets, and no pets are allowed inside. 

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