GMAT Verbal : Identifying Causal Flaws

Study concepts, example questions & explanations for GMAT Verbal

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Example Questions

Example Question #3 : Parallel Reasoning

All English Springer Spaniels have long hair. All Rottweilers have short hair. Each of Tina's dogs is a cross between an English Springer Spaniel and a Rottweiler. Therefore, Tina's dogs have medium-length hair.

Which one of the following uses flawed reasoning that most closely resembles the flawed reasoning used in the argument above?

Possible Answers:

All economists know linear algebra. All physicists know relativistic mechanics. Wilma is both an economist and a physicist. Therefore, Wilma knows both linear algebra and relativistic mechanics.

All halogen gases are toxic to humans. All non-radioactive noble gases are non-toxic to humans. "Nobagen" gas is a mixture of a halogen gas and a noble gas. Therefore, "nobagen" gas is moderately toxic to humans.

All players on the Wildcats have brown hair. All players on the Razorbacks have red hair. Members of the Moye family are on both the Wildcats and the Razorbacks. Therefore, some members of the Moye family have brown hair and others have red hair.

All cars made by Chord are very well made. All cars made by Fysler are very poorly made. Half of the cars on Jim's lot are very well made and the other half are very poorly made. Therefore, half of the cars on Jim's lot are Chords and half are Fyslers.

All typists who practice at least one hour per day can type one hundred words per minute. But some typists who do not practice can also type one hundred words per minute. Mike, a typist, practices thirty minutes per day. Therefore, Mike types fifty words per minute.

Correct answer:

All halogen gases are toxic to humans. All non-radioactive noble gases are non-toxic to humans. "Nobagen" gas is a mixture of a halogen gas and a noble gas. Therefore, "nobagen" gas is moderately toxic to humans.

Explanation:

The flawed reasoning used in the passage is that a combination of two "parent" items with different attributes necessarily yields a "child" product having attributes that are averages of its parents' attributes. The correct answer uses parallel reasoning inasmuch as the argument uses the fact that halogen and noble gases differ with respect to toxicity to conclude that a combination of such gases would yield a gas having toxicity that is the average of the toxicity of its "parent" gases.

Example Question #2 : Critical Reasoning

After replacing her old air conditioner with a new, energy-efficient unit, Paula’s electric bills increased.

Each of the following, if true, contributes to an explanation of the increase mentioned above EXCEPT:

Possible Answers:

Soon after the new air conditioner was installed, Paula adopted a child, doubling the size of her household.

Paula installed an electricity-intensive indoor tanning bed after she replaced her air conitioning unit.

The new air conditioner uses a smaller share of the electricity used by Paula’s home than did the old unit.

Paula's electricity costs increased by 15 cents per kilowatt hour after she replaced her air conditioner.

Following the installation of her new air conditioner, Paula's neighborhood experienced a prolonged and severe heat wave, requiring heavy use of the new unit.

Correct answer:

The new air conditioner uses a smaller share of the electricity used by Paula’s home than did the old unit.

Explanation:

The correct answer here is the one that does not explain the apparent paradox. That the new unit uses a smaller share of total electricity is consistent with its being more energy efficient. It does not explain how her electric bills could have gone up despite her installation of the more effeicient unit; all other answers provide possible resolutions of such apparent paradox.

Example Question #3 : Critical Reasoning

Advertisement: Coma Cola is the best-tasting cola on the market and we conducted a test using over 1000 cola consumers to prove it. Each consumer was given two identical cups filled with a carbonated beverage from the same fountain. One cup was filled with Coma Cola and the other was filled with unadulterated soda water. Ninety-nine percent of the consumers preferred the Coma Cola. So, Coma Cola is the best tasting cola available.

The advertisement’s reasoning is most vulnerable to criticism on the grounds that it fails to consider whether ___________________

Possible Answers:

The consumers tested had the opportunity to evaluate colas other than Coma Cola.

Coma Cola is cheaper or more expensive than other colas.

Any portion of the population is allergic to any of the ingredients in Coma Cola.

The consumers tested had the opportunity to evaluate flavored soft drinks other than colas.

Coma Cola has more or less caffeine than other colas.

Correct answer:

The consumers tested had the opportunity to evaluate colas other than Coma Cola.

Explanation:

The advertisement's claim, that Coma Cola is the best tasting cola, is based on 99% percent of cola consumers choosing it over soda water. The flaw in the experimental setup is that just because a consumer chooses Coma Cola over soda water, it does not mean that she will choose Coma Cola over any other cola, let alone over all other colas. 

The correct answer recognizes that, in order to validly make such a claim, one would have to show a preference for Coma Cola over other colas, not over soda water (or even over other flavored soft drinks, as one of the incorrect answer choices indicates).

Example Question #4 : Critical Reasoning

Eggplants are always purple. John bought a purple vegetable. Therefore, it was an eggplant. 

Which of the following arguments contains reasoning most similar to the flawed reasoning in the above argument?

Possible Answers:

Jenny always eats healthy. Salmon is a healthy food. Therefore, she eats salmon. 

Bluebirds are not always blue. A brown bird was outside the window. Therefore, it may or may not have been a blue bird. 

Except for 2, prime numbers are always odd. The number 13 is odd. Therefore, it is prime. 

Gambling is a risky hobby. Jamie likes taking risks. Therefore, she likes to gamble. 

Rabbits are fast creatures. A fast creature ran by. Therefore, it may have been a rabbit. 

Correct answer:

Except for 2, prime numbers are always odd. The number 13 is odd. Therefore, it is prime. 

Explanation:

In this argument, the flaw is framed in the following way:

X is always Y. A is Y. Therefore, A is X.

(Just because X is always Y does NOT mean that Y is always X.)

The flawed argument is therefore most like:

Except for 2, prime numbers are always odd. The number 13 is odd. Therefore, it is prime. 

Here

x= prime numbers

Y = odd

A = 13

The structure of this argument is the same as the structure argument in:

Eggplants are always purple. John bought a purple vegetable. Therefore, it was an eggplant. 

X= eggplants

Y = purple

A = purple vegetable

Example Question #5 : Critical Reasoning

Two students were given practice exams. One exam ordered the questions from hardest to easiest, while the other exam ordered the questions from easiest to hardest. The student who took the test with questions ordered hardest to easiest performed more poorly than the other student. Therefore, tests that ordered hardest to easiest will cause a student to perform more poorly.

This argument is most vulnerable to criticism if which of the following statements is true?

Possible Answers:

The student who performed more poorly has a lower grade point average than the other student. 

The students took the exam in different classrooms, one of which was more spacious. 

One student was from Los Angeles, while the other student was from New York. 

The students had the same grade point averages. 

The test consisted solely of math questions, rather than being a blend of content. 

Correct answer:

The student who performed more poorly has a lower grade point average than the other student. 

Explanation:

The conclusion of this argument is that when questions are ordered hardest to easiest, students perform more poorly on them. In order to refute this causal assertion, another source of the poor performance must be introduced. The fact that the student who performed more poorly has a lower grade point average than the other student is a significant intervening cause, and therefore the correct answer. 

Example Question #6 : Critical Reasoning

Thousands of people contract tonsillitis every year, and yet all go on to live normal lives after the operation. We can conclude, from this observation, that the tonsils have no function in the body.

The argument would be most weakened by which of the following, if it were true?

Possible Answers:

People live normal lives after appendectomies, but the appendix is known to be part of the digestive system. 

Another part of the body can take over the function of the tonsils if they are removed.

The human tonsil develops as part of the immune system, a system of vital importance in defense against disease. 

Tonsillectomies are performed only when the tonsils become seriously infected.

The tonsils have been shown to have a vital role to play in the physiology of laboratory rabbits and mice. 

Correct answer:

Another part of the body can take over the function of the tonsils if they are removed.

Explanation:

The conclusion states that the tonsils have no function in the body. To weaken this conclusion, we should try to show that the tonsils do in fact have a function, at least at some point in human life. Comparison with another organ is not really useful, as they might be very different from tonsils, and what happens in other animals is also not directly relevant. And discussing where the tonsils develop has nothing to do with their function. Finally, though an organ might develop as part of a system and yet have no function (like the appendix or muscles that wiggle the ear), the only answer left suggests there is a function even though this function can be taken over by another part of the body. This suggestion most weakens the argument posed above.

Example Question #7 : Critical Reasoning

According to an article in a nutritional magazine, eating beets significantly lowers the risk of cancer. The article refers to a study that found that people who consumed one or more beets per day were half as likely to be diagnosed with cancer as people who did not.

Which of the following, if true, most weakens the argument in the magazine article?

Possible Answers:

Another study found that people who consumed one tablespoon of fish oil per day were more than four times less likely to be diagnosed with cancer as those who did not.

The participants in the study who ate beets were more likely to exercise regularly than those who did not eat beets.

In another experiment, cancer patients who ate one or more beets per day were no more likely to recover than those who ate no beets.

Participants in the study reported consuming no vegetables other than beets.

The study was only conducted in one city.

Correct answer:

The participants in the study who ate beets were more likely to exercise regularly than those who did not eat beets.

Explanation:

Because study participants who ate beets were also more likely to exercise regularly than those who did not eat beets, it is impossible to determine whether beets or regular exercise were more influential in preventing cancer. Thus this is the correct answer.

Example Question #8 : Critical Reasoning

Students from outside the province of Merryweather, who in any given academic year pay twice as much tuition each as do students from within Merryweather, had traditionally accounted for at least two-thirds of the enrollment at Central Merryweather College. Over the past  years academic standards at the college have risen, and the proportion of students who are not from Merryweather has dropped to around .

Which one of the following reasonably be inferred from the statements above?

Possible Answers:

Over the past  years the number of students from Merryweather increased and the number of students from outside Merryweather decreased.

If it had not been for the high tuition paid by students from outside Merryweather, the college could not have improved its academic standards over the past  years.

Over the past  years academic standards at Central Merryweather College have risen more than academic standards at any other college in Merryweather.

If the college’s per capita revenue from tuition has remained the same, tuition fees have increased over the past  years.

If academic standards had not risen over the past  years, students who are not from Merryweather would still account for at least two-thirds of the college’s enrollment.

Correct answer:

If the college’s per capita revenue from tuition has remained the same, tuition fees have increased over the past  years.

Explanation:

Since we cannot say what was responsible for the increased academic standards, we can rule out any attempt to explain it. It could be that more residents of Merryweather began to attend the school, as opposed to a reduction in those from outside Merryweather, or vice versa, so avoid explanations as to why the population decreased.
The only thing we can infer from the information given is that there could be tuition increases if per capita revenue remained the same: Say students not from Merryweather used to account for  and were paying, for example,  in total for tuition, if they now account for , they must pay a higher tuition to maintain a stable per capita revenue.

Example Question #1 : Identifying Causal Flaws

A medical degree is necessary for appointment to the hospital's board of directors. Further, no one having more than a five-percent equity stake in a pharmaceutical company can be appointed to the board of directors. Consequently, Dell, a practicing physician with a PhD in bioethics, cannot be appointed the hospital's treasurer, since he owns fifteen percent of PillCo, a pharmaceutical company.

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

Possible Answers:

If Dell sold his stake in PillCo, he would be appointed treasurer.

Only those eligible for appointment to the hospital's board of directors can be appointed as the hospital's treasurer.

A PhD is not necessary for appointment to the position of treasurer.

Anyone with a medical degree who does not hold more than a five-percent stake in any pharmaceutical company is eligible for appointment to the hospital's board of directors.

PillCo is one of the hospital's pharmaceutical vendors.

Correct answer:

Only those eligible for appointment to the hospital's board of directors can be appointed as the hospital's treasurer.

Explanation:

To answer this question, it is necessary to recognize that while appointment criteria are set forth for the board of directors, they are applied to the position of Treasurer. We are never told that a Treasurer is a member of the board of directors. Thus, the conclusion is only warranted if eligibility for appointment to the board is a necessary condition for appointment to the position of Treasurer.

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