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 #21 : Lsat Logical Reasoning

The promise of this scientific research is that soon brainpower can be altered to better reflect the processes by which a computer sorts information. This will mean that rather than seeking to make computers more like humans, humans will move closer to being like computers.

Based on the information in the passage, it can be inferred that it must be true that __________.

Possible Answers:

computers use information in a way that directly relates to human brain functions

humans all wish to think much more like computer

computerized methods of processing information are much less complex than human thought

humans do not fully understand how to think like computers

human brains and computers do not process information in the same manner

Correct answer:

human brains and computers do not process information in the same manner

Explanation:

The passage states that the research is trying to make human brainpower be more like a computer process. This means that what can be stated for certain based on the information in the passage is that computers and humans do not process information in the exact same way.

Example Question #21 : Must Be True

Most dachshunds have legs less than four inches long. Most dachshunds have long faces. Some animals with long faces make great pets. If an animal has legs less than four inches long, then it will not be a fast runner. Some animals are friendly.

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

Possible Answers:

Some animals with legs less than four inches long have long faces.

Most great pets have long faces.

Most animals are friendly.

Most animals with long faces make great pets.

Most animals with long faces are Dachshunds.

Correct answer:

Some animals with legs less than four inches long have long faces.

Explanation:

The answer is correct because there are overlapping "most" statements. From the stimulus, we can conclude that some animals with legs less than four inches long have long faces.

Example Question #23 : Determining Which Answer Must Be True Based On The Information Given

If all stores closed on Christmas Day, I would not have been able to buy groceries for dinner. If I had been unable to buy groceries, the children would certainly have cried. Fortunately, in the end, none of the children cried. 

Which of the following conclusions can properly be inferred from the information above?

Possible Answers:

No stores closed on Christmas Day.

If any of the children cried that night, I had been unable to buy groceries.

Some stores remained open on Christmas Day.

None of the stores remained open on Christmas Day. 

I purchased all of my groceries on Christmas Day.

Correct answer:

Some stores remained open on Christmas Day.

Explanation:

By following the logic chain, it is clear that the children would have cried if none of the stores remained open. Since they did not cry, we know that at least some of the stores did stay open.

Example Question #22 : Must Be True

If a ruling party both reduces the unemployment rate and prevents major acts of terrorism, then the party’s rule will maintain power. A ruling party can still maintain power even if it does not maintain high levels of government spending. The current ruling party has not maintained high levels of government spending but has prevented major acts of terrorism.

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

Possible Answers:

In order to maintain power, the ruling party must prevent minor acts of terrorism.

The current ruling party will not maintain power.

The current ruling party has reduced the unemployment rate.

If the ruling party keeps inflation low, then it will maintain power.

If the present administration reduces the unemployment rate, then it will maintain power.

Correct answer:

If the present administration reduces the unemployment rate, then it will maintain power.

Explanation:

Because the question is asking us what must be true, we are looking for an answer that is guaranteed to be correct under all situations. We do not know whether the current ruling party has reduced the unemployment rate and we do not know if the sufficient conditions for maintaining power have been met. We do however know that because the current ruling party has prevented major acts of terrorism, if they are able to reduce the unemployment rate, they will maintain power.

Example Question #21 : Inference

All scientists are studious. Some people who are studious are rich. If someone is rich they are able to live comfortably. Most people who are studious have trouble focusing.

If the above statements are true, all of the following must be true, EXCEPT

Possible Answers:

Some people who have trouble focusing are studious.

Some studious people are scientists.

All people who are rich are able to live comfortably.

Some rich people are studious.

Some scientists are rich

Correct answer:

Some scientists are rich

Explanation:

The correct answer follows from the stimulus. It is the only answer that does not have to be true.

Example Question #21 : Must Be True

Every teacher expects their students to finish their homework. Any student that does not finish their homework gets detention. No student in detention is allowed to participate in school sporting events. All school sporting events take place on weekends. 

Which of the following must be true?

Possible Answers:

Every student that meets their teachers' expectations can participate in weekend sporting events.

No student that serves detention has violated their teachers' expectations.

No student that has completed their homework serves detention.

Every teacher expects their students to participate in school sporting events.

Every student that does not complete their homework cannot participate in weekend sporting events.

Correct answer:

Every student that does not complete their homework cannot participate in weekend sporting events.

Explanation:

This is the only answer the can truly be inferred from the information above. A student that does not complete their homework gets detention. Any student that gets detention cannot participate in sporting events, which take place on weekends. 

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