Necessary Assumption
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LSAT Logical Reasoning › Necessary Assumption
Researchers found that people who drink green tea daily have a lower risk of developing heart disease. Therefore, drinking green tea is a key factor in reducing the risk of heart disease. Which one of the following assumptions is required by the argument?
The study controlled for other factors that affect heart disease risk.
People who drink green tea also engage in other healthy behaviors.
The reduced risk of heart disease is primarily due to green tea consumption.
People who drink green tea prefer it over other beverages.
Green tea contains specific compounds that reduce heart disease risk.
Explanation
The argument concludes that drinking green tea is a key factor in reducing heart disease risk, based on research showing daily green tea drinkers have lower heart disease risk. The logical gap involves inferring causation and primacy from correlation. For this argument to work, we must assume that the reduced risk is primarily due to green tea consumption rather than other factors. Choice C addresses this assumption about green tea being the primary causal factor. Choice B, while tempting, only provides a potential mechanism but doesn't establish primacy—the argument could work even without knowing the specific compounds involved. The negation test confirms necessity: if the reduced risk was NOT primarily due to green tea consumption, then green tea wouldn't be a "key factor" as claimed, defeating the argument's central conclusion.
A coffee chain tested a new training program in ten stores and found that customer complaints dropped by about 20% over the next month. In those same stores, managers reported that employees began greeting customers more consistently, a behavior the training emphasized. Because consistent greetings make customers feel acknowledged, the training program is what reduced complaints. So the chain should roll out the program companywide to reduce customer complaints across all its stores.
Employees at the test stores liked the new training program.
No other factors besides the training could possibly influence customer complaints.
The training program will reduce complaints by at least 20% in every store.
In the test stores, customer complaints dropped by about 20% after the program began.
The ten test stores are representative of the chain’s stores in ways relevant to customer complaints.
Explanation
This argument concludes that the coffee chain should roll out a training program companywide based on results from ten test stores. The premises show complaints dropped 20% and employees improved their greeting behavior. The logical gap lies between the test results and the broad recommendation: for the companywide rollout to succeed, the ten test stores must accurately represent the chain's other stores in relevant ways. If the test stores were atypical—perhaps in areas with unusually receptive customers or different demographics—the training might not work elsewhere. Choice (C) simply restates the test results, while choice (E) eliminates confounding variables but doesn't address representativeness. Using the negation test on (A): if the test stores weren't representative in relevant ways, we couldn't reliably predict the training's success elsewhere, undermining the argument's recommendation.
Which one of the following assumptions permits the conclusion above to be properly drawn?
Temperature, light, and soil nutrients will be identical in the greenhouse and at high altitude.
Greenhouses maintained at low humidity are inexpensive to operate.
The species is more valuable when it has thicker leaves.
Leaf thickness in this species varies in response to humidity rather than being fixed genetically in high-altitude populations.
High ultraviolet radiation at high altitude does not harm this species.
Explanation
The conclusion requires that leaf thickness is environmentally responsive to humidity, not genetically fixed. If thickness is not affected by humidity, lowering it would not cause thicker leaves.
Which one of the following assumptions permits the conclusion above to be properly drawn?
E. Emissions from private cars on Main Street are not, apart from bus-related spikes, a significant source of downtown air pollution.
B. Main Street's traffic volume has increased in recent years.
A. Bus schedules will remain unchanged after the car ban is implemented.
D. The city's air monitors accurately record downtown pollution spikes.
C. The car ban will not increase bus idling at the station.
Explanation
To infer that banning cars will not significantly improve air, the argument must assume car emissions are not a substantial source aside from bus-related spikes. The other choices are ancillary and, if false, would not necessarily undermine the conclusion.
The argument above depends on which one of the following assumptions?
The museum will continue to accept group reservations at the new price.
The modest price increase will not cause most tourists to cancel plans to visit the museum.
Local residents will be unaffected by the price increase.
The museum's exhibits will not change next quarter.
Competing attractions will not lower their prices next quarter.
Explanation
For attendance to remain steady, the tourists who make up most visitors must not be deterred by the small price increase. The other choices are either irrelevant or merely supportive but not required.
Which one of the following assumptions permits the conclusion above to be properly drawn?
The study at Firm Q used validated productivity measures.
Supervisors can provide quiet spaces without large capital expense.
Most employees will choose to use the nap period.
Employees who do not nap will not resent those who do.
Allowing a nap period will not reduce total working time so much that aggregate output falls.
Explanation
The argument assumes the time cost of naps will not outweigh efficiency gains; if naps cut too much working time, overall output could drop. The other options might help the policy succeed but are not required for the conclusion.
Which one of the following assumptions permits the conclusion above to be properly drawn?
The current annual audits will be discontinued when random audits begin.
The random audits will be conducted by an independent outside firm.
Employees will be made aware that audits will occur at random times.
Punishments for fraud at the company will be severe.
The cost of instituting random audits will be acceptable to the company.
Explanation
Random audits can deter fraud only if employees know they might be audited unexpectedly. The other options may strengthen or concern feasibility but are not required for deterrence.
Which one of the following assumptions permits the conclusion above to be properly drawn?
Piano lessons are more popular among students than violin lessons.
The district can afford to purchase additional pianos if needed.
The math test used in the study did not change format between administrations.
Most math teachers support incorporating music into the school day.
Most students will in fact complete the required daily piano practice.
Explanation
The prediction relies on students actually doing the practice, so compliance is required. If most students do not practice, the expected improvement may not occur, defeating the conclusion. The other choices are irrelevant or merely strengthen without being necessary.
The argument above depends on which one of the following assumptions?
Faculty will devote additional time to editing and improving recorded lectures.
The cost savings from moving lectures online will be substantial.
Small seminar courses will continue to meet in person.
Most students have reliable access to the technology needed to view and use recorded lectures.
Students prefer online lectures to in-person lectures for large courses.
Explanation
The mechanism cited—benefits of pausing and replaying—requires that students can actually access and use recordings. The other options may support or are tangential but are not necessary for the conclusion about learning outcomes.
The argument above depends on which one of the following assumptions?
The survey used a random sample of festival attendees rather than chefs.
The festival chefs do not differ markedly from most chefs nationwide in their preferences for spice X.
The surveyed chefs answered the questions honestly.
Consumers nationwide enjoy the flavor of spice X.
Most chefs define 'prefer' in the same way.
Explanation
Generalizing from festival chefs to most chefs nationwide requires that festival chefs are not atypical in this preference. If they are systematically different, the survey would not support the national conclusion.