LSAT Quiz: Sufficient Assumption

What this quiz covers

This quiz focuses on Sufficient Assumption, giving you a quick way to practice the rules, question types, and explanations that matter most for LSAT.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The curator is generally careful to consult the board on significant loans.
2. Any loan requiring board approval cannot be approved by the curator. (correct answer)
3. The regional gallery cannot insure paintings valued at over one million dollars.
4. The curator has previously approved loans of similar works by Lucent.
5. The board was not in session at the time the loan was approved.

Explanation: To conclude the painting is not over one million, we must rule out that the approved loan required board approval; assuming the curator cannot approve such loans ensures that. The other options are about habits, logistics, or timing and do not make the conclusion certain.

Question 2

1. The council will implement the passed recommendations efficiently.
2. The auditor made no recommendations other than 1 through 4. (correct answer)
3. The auditor's recommendations have eliminated waste in other cities.
4. Recommendations 1 through 4 are the most important ones.
5. The council plans to consider additional reforms next year.

Explanation: The conclusion requires that the council adopted all of the auditor's recommendations; this is guaranteed only if there were no recommendations beyond 1–4. The other choices either strengthen or add irrelevant information but do not ensure that all recommendations were adopted.

Question 3

1. The Gazette employs editors who verify scientific claims before publication.
2. No reader wrote a letter pointing out any error in the lead story.
3. The Gazette followed its correction policy in the issues published after that lead story. (correct answer)
4. Most readers would have noticed a correction if one had been published.
5. The assertion that Mars has rings appears in the headline as well as the article.

Explanation: The reasoning depends on inferring truth from the absence of a correction, which requires that the paper actually followed its policy. Choice C supplies that, so no correction implies no factual error and thus a true assertion. The other options do not ensure that absence of a correction tracks truth.

Question 4

1. The budget cuts that reduce funding for other anti-burglary measures will not be permanent and will be restored within the coming fiscal year.
2. The Neighborhood Patrol program is substantially less expensive to run than the other anti-burglary efforts our city currently maintains and funds.
3. Our city has burglary patterns broadly similar to those in the communities studied during the multi-city evaluation of the program.
4. Implementing the Neighborhood Patrol program is by itself sufficient to cause a drop in burglary within six months, even if other anti-burglary measures are reduced. (correct answer)
5. Residents across our city will volunteer to participate in the Neighborhood Patrol program at rates comparable to those seen elsewhere.

Explanation: The argument concludes that burglary will drop, but it also tells you that funding for other anti-burglary measures will be cut. That is the gap: maybe the reductions elsewhere will offset any benefit from the program. The claim that the program by itself is sufficient to cause a drop within six months even when other measures are reduced closes exactly this gap, so the conclusion follows. That the budget cuts will later be restored does not help, because the drop must happen within six months and the argument is about the period of reduced funding. That the program is cheaper than other efforts speaks to cost, not to whether burglary actually falls. That our city resembles the evaluation communities in burglary patterns is tempting, but the evaluation communities were not described as cutting other measures, so similarity alone cannot guarantee the drop here. That residents will volunteer at high rates might help the program work, but it is not enough to overcome the possible loss from the cuts, so it does not make the conclusion properly drawn. Only the sufficiency claim guarantees the result despite the reductions.

Question 5

1. Enough commuters will use the additional express routes next quarter to lower the citywide average commute time. (correct answer)
2. The new express routes will run on time throughout next quarter.
3. Most commuters value shorter trips over the ability to sit during the ride.
4. No major road construction projects will begin next quarter.
5. The additional express routes will connect the city's most heavily traveled origin-destination pairs.

Explanation: The gap is from route-specific time savings to a citywide average reduction; that requires sufficient adoption. A guarantees average times drop; the others at best strengthen or are tangential and do not ensure a citywide decrease.

Question 6

1. The airspace directly above public roads is public property owned and controlled by the same government that maintains those roads.
2. Drones flown in the airspace above public roads are already subject to a comprehensive set of federal aviation regulations.
3. Operating in the airspace above public roads counts as being operated on public roads for purposes of the statute. (correct answer)
4. The term 'roads' as used throughout the statute includes the bridges and tunnels that cars regularly travel across.
5. Drones operating overhead can distract, injure, or otherwise endanger the drivers traveling on the public roads below.

Explanation: The argument moves from drones being operated 'in the airspace above public roads' to the statute, which covers vehicles 'operated on public roads,' applying to them. The missing link is whether operation above the road legally counts as operation on the road. The correct answer supplies exactly that: it equates operating in road airspace with being operated on public roads for the statute's purposes, so the conclusion follows. The choice about airspace being public property tells us who owns the space, but ownership does not make flying above equal to operating on the road. The choice about existing federal aviation regulations adds a separate legal regime and does nothing to bridge 'above' and 'on.' The choice expanding 'roads' to bridges and tunnels stretches a different term and still leaves drones flying above, not on, any surface. The choice about drones endangering drivers offers a policy reason to regulate them, but danger is not the statute's trigger—location of operation is. Only one choice closes the specific gap between operating above the road and operating on it.

Question 7

1. If any other environmental project was implemented in June, then that project, not the filtration system, lowered the pollution level.
2. If the filtration system operated throughout June, then it was functioning properly rather than merely running idle.
3. If residents noticed clearer water in June, then the filtration system was the cause of that improvement.
4. If the lake's pollution level decreased in June, then that decrease was caused by the newly installed filtration system. (correct answer)
5. If the monitoring instruments were calibrated in May, then their June readings certainly reflected the water accurately.

Explanation: The premises establish that pollution decreased in June (since the instruments did not malfunction), but they never connect that decrease to the filtration system. To reach the causal conclusion, you need a bridge that says any June decrease was caused by the new filtration system — exactly what the keyed choice supplies. The option about other environmental projects works the wrong direction: it hands the cause to a different project, undermining the intended conclusion rather than securing it. The option that the system was functioning properly rather than idle only tells you the machine worked; it never links that operation to the observed drop in pollution. The option about residents noticing clearer water starts from an unstated observation and, even if true, offers no guarantee the decrease itself was caused by the system. The option about May calibration speaks to instrument accuracy, which the certification already covers, and says nothing about what caused the pollution to fall. Only the keyed assumption guarantees the causal leap the argument requires.

Question 8

1. Tonight, there are no temporary traffic restrictions on Main Street that would prevent vehicles with current inspections from being driven there. (correct answer)
2. Leo prefers to drive his own car tonight rather than take the bus or ride with a friend to the Main Street library.
3. The parking garage nearest the Main Street library will remain open and available to visiting drivers until well past midnight tonight.
4. Main Street usually carries relatively light vehicle traffic during weekday evening hours, especially near the public library entrance.
5. Leo's car, aside from its current inspection status, is in sound mechanical condition and fully capable of the drive tonight.

Explanation: The argument moves from a general rule (inspected cars may be driven on Main Street) to a specific conclusion about tonight. But the passage warns that the city sometimes imposes temporary restrictions for parades or construction. To guarantee the conclusion, you must rule out any such restriction tonight — that is exactly what the correct answer does, closing the only gap between the rule and the conclusion. Whether Leo prefers driving over the bus or a ride is irrelevant to whether he is permitted to drive; permission does not depend on preference. Whether the parking garage stays open concerns where he parks, not whether he may lawfully drive on the street. Whether Main Street usually has light evening traffic describes convenience, not permission, and 'usually' says nothing about tonight's actual restrictions. Whether the car is mechanically sound may matter for safety, but the policy grants permission based on a current inspection, not on mechanical condition. Only ruling out tonight's restrictions makes the conclusion follow.

Question 9

1. The physicians deciding among these treatments are already aware of the results reported in the recent Medora clinical trials.
2. Medora's manufacturer will secure coverage under most major insurance plans before physicians begin routinely prescribing it.
3. No current competitor will improve its own therapeutic index enough to overtake Medora's within the near term.
4. If there is no approved generic of Medora's compound, then there is no cheaper generic alternative physicians would consider substitutable for Medora. (correct answer)
5. Medora's manufacturing costs will remain stable enough over the next year to keep its market price competitive.

Explanation: The rule says physicians prefer a treatment only when the exception fails to hold — that is, only when there is no cheaper generic alternative. The passage establishes there is no approved generic of Medora's compound, but 'no approved generic of the compound' is not the same as 'no cheaper generic alternative.' The correct answer bridges exactly that gap: if the absence of an approved generic means no cheaper generic substitute exists, then the exception is ruled out and the conclusion follows. The choice about physicians being aware of the trial results may seem practical, but the argument concerns what physicians will prefer given the criteria, not their information. The insurance-coverage choice adds a real-world consideration the rule never mentions. The choice about a competitor improving its index later addresses a future scenario, not the present comparison the trials already settled. The manufacturing-cost choice touches price, but stable costs do not tell us whether a cheaper generic substitute currently exists. Only the bridging assumption makes the conclusion properly drawn.

Question 10

1. The filters will be maintained according to the manufacturer's specifications, so the promised 90 percent reduction is actually achieved rather than gradually eroding over time.
2. No other factory in the region plans to increase its particulate emissions by an amount that would offset the reduction achieved at the largest factory next month.
3. Prevailing winds do not blow significant particulate matter into the region from outside sources such as neighboring industrial areas or distant wildfires.
4. The factory's current emissions are sufficient to cause the region's exceedances, and reducing that factory's emissions by about 90 percent will bring total regional particulate levels below the legal limit. (correct answer)
5. Local traffic contributes less particulate pollution to the region's overall air quality than the largest factory currently does before its new filters begin operating.

Explanation: The argument leaps from a big cut at one source to region-wide compliance. To make that leap valid, two things must hold: the factory's emissions must actually be what pushes the region over the limit, and removing 90 percent of them must be enough to drop total levels below the limit. The choice stating exactly this fills the gap and guarantees the conclusion. Maintaining the filters to spec ensures the reduction happens, but even a full 90 percent cut might not bring the region into compliance if other sources already exceed the limit—so it isn't sufficient. Ruling out increases at other factories prevents new emissions from erasing the gain, yet the existing baseline could still exceed the limit; it doesn't guarantee compliance. Ruling out particulates blown in from outside removes one external source, but says nothing about whether the remaining local total falls below the limit. Comparing local traffic to the factory only ranks two contributors; even if the factory emits more, cutting it 90 percent need not bring the total under the legal ceiling. Only the choice tying the factory's emissions directly to the exceedance AND to sufficiency for compliance makes the conclusion properly drawn.

Question 11

1. Farmers will comply with application guidelines provided by the board.
2. X is less expensive than existing herbicides used against kudzu.
3. At the planned field application levels, X both kills kudzu under field conditions and does not harm corn plants. (correct answer)
4. Kudzu in the region has not developed resistance to herbicide X.
5. Spraying can be completed before the start of the rainy season.

Explanation: The gap moves from lab efficacy to field efficacy and crop safety. C supplies both under real conditions, making the conclusion follow; the other choices may help but do not ensure both eradication and lack of crop damage.

Question 12

1. The transit policy will not increase emissions from buses beyond current levels.
2. Factories and buildings will not increase their emissions this year.
3. Air quality improvements, once achieved, persist for more than a year.
4. The city's population will not grow substantially this year.
5. Reducing car trips by 10 percent will reduce the city's greenhouse gas emissions by at least 10 percent within the year. (correct answer)

Explanation: The gap is between fewer car trips and a 10 percent emissions decline; the correct assumption equates the two at the needed magnitude. The other options address potential offsets or context but do not ensure the threshold decline required for the rule to trigger.

Question 13

1. The employees who used the software were not inherently more efficient than those who did not. (correct answer)
2. The tasks completed by employees using the software were of similar complexity to those not using it.
3. The software was the only new tool introduced during the test period.
4. The employees using the software received adequate training on its use.
5. The test was conducted under controlled conditions to ensure accuracy.

Explanation: The technology company claims its software increases productivity by 20% based on employees using the software completing tasks faster. The critical gap involves potential selection bias: perhaps more skilled or efficient employees were chosen to test the software, or volunteers were inherently better performers. To establish that the software (not employee characteristics) caused the improved performance, we need to eliminate this alternative explanation. Choice A provides this assumption by stating that employees using the software were not inherently more efficient than those who didn't. This ensures that the observed performance difference stems from the software itself rather than pre-existing employee capabilities. Choice C addresses whether the software was the only new tool but doesn't eliminate the possibility that better employees were selected for testing. Sufficient assumptions in productivity studies must eliminate participant selection bias.

Question 14

1. The new teaching strategy was the only change in the curriculum during the year.
2. The increase in reading scores was not due to other educational interventions. (correct answer)
3. Students' reading material difficulty level did not change during the year.
4. Teachers were adequately trained to implement the new strategy.
5. Student engagement in reading activities increased with the new strategy.

Explanation: The school district concludes that the new teaching strategy was effective based on a 15% increase in reading scores after implementation. The logical gap is that many factors could contribute to improved reading scores during a school year—other educational interventions, different teachers, new materials, or natural student development. To establish that the teaching strategy specifically caused the improvement, we need to eliminate these alternative explanations. Choice B provides this assumption by stating the increase was not due to other educational interventions. This isolates the new teaching strategy as the cause of improvement. Choice A claims the strategy was the only curriculum change, but this doesn't address other potential educational interventions outside the curriculum. Sufficient assumptions in educational effectiveness arguments must eliminate competing educational causes.

Question 15

1. The study accounted for other factors that could influence susceptibility to colds. (correct answer)
2. Vitamin C is the only nutrient that influences the immune system's effectiveness.
3. Participants who took vitamin C had similar health conditions to those who did not.
4. The amount of vitamin C taken by participants was consistent throughout the study.
5. Colds experienced by participants were not of varying severity.

Explanation: This causal argument claims that vitamin C prevents colds based on a study showing 30% fewer colds among vitamin C users. The fundamental gap is that this correlation alone doesn't prove causation—other factors might explain why vitamin C users had fewer colds. Perhaps people who take vitamin C also eat better, exercise more, or have different health habits. To make the causal conclusion logically certain, we need to assume that such confounding variables were controlled for. Choice A does exactly this by assuming the study accounted for other factors that could influence cold susceptibility. With this assumption, vitamin C becomes the only explanation for the observed difference. Choice C addresses similarity between groups but doesn't eliminate other causal factors. The crucial principle here is that sufficient assumptions in experimental contexts must eliminate confounding variables to establish definitive causation.

Question 16

1. If a route's arrival times become more reliable for any reason, then overall satisfaction with the transit system increases across all commuters who use that route.
2. If a dedicated lane is added to a route and its arrivals become more reliable, then the added lane increases overall satisfaction with the transit system. (correct answer)
3. If a route's arrivals become more reliable, then no factor other than the addition of a dedicated lane could possibly have been responsible for that improvement.
4. If overall satisfaction with the transit system increases, then a dedicated lane must have been added to at least one route somewhere in the city.
5. If a route receives a dedicated lane, then the city usually also assigns newer buses to that route, further improving commuter satisfaction over time.

Explanation: The conclusion claims that adding the dedicated lane to Route 7 will increase overall satisfaction. The premises give you two links—dedicated lanes improve reliability, and reliability improvements raise satisfaction by reducing early departures—but they never directly guarantee that this particular lane addition produces the satisfaction increase. The correct answer bridges exactly that gap: if a lane is added and reliability rises (both true for Route 7), then the added lane increases satisfaction. That guarantees the conclusion. The option tying reliability from any cause to satisfaction covers the reliability-to-satisfaction step but never credits the lane addition itself, so it cannot deliver the conclusion about adding the lane. The option insisting no factor other than a lane could cause reliability runs the causation backward and is irrelevant to whether satisfaction rises. The option saying satisfaction only occurs when a lane is added states a necessary condition, not a sufficient one, so it cannot force the conclusion forward. The option about newer buses introduces an outside factor that is neither established nor needed, and it argues satisfaction from a different cause. Only the second option makes the specific lane-to-satisfaction inference the conclusion requires.

Question 17

1. There are no other significant environmental changes affecting the bird population. (correct answer)
2. Pesticides used in the area are harmful to birds.
3. Bird species in the area are sensitive to changes in their environment.
4. The area has experienced similar declines in other wildlife populations.
5. Pesticide usage in the area has increased more than in other regions.

Explanation: The environmental scientist argues that increased pesticide use caused the bird population decline based on correlation between pesticide usage and population decline. The logical gap is that correlation doesn't prove causation—other environmental factors could explain the bird population decline during the same period. To make this causal conclusion logically certain, we need to eliminate alternative environmental causes. Choice A provides this crucial assumption by stating there are no other significant environmental changes affecting the bird population. With this assumption, pesticides become the only explanation for the decline. Choice B merely states that pesticides are harmful to birds, which supports the possibility of harm but doesn't eliminate other causes. The key insight is that sufficient assumptions in environmental causation arguments must rule out competing environmental factors to establish definitive cause-and-effect relationships.

Question 18

1. People who consume less sugar do not have other risk factors for diabetes.
2. Reducing sugar intake is the most effective way to lower diabetes risk.
3. The study accounted for other dietary factors influencing diabetes risk. (correct answer)
4. Sugar consumption levels in the study were consistent among participants.
5. Diabetes rates are not affected by factors unrelated to diet.

Explanation: The health organization concludes that reducing sugar intake decreases diabetes risk based on correlation between high sugar consumption and increased diabetes rates. The logical gap is that this correlation alone doesn't establish causation—other dietary or lifestyle factors might be the real cause. People with high sugar intake might also have poor overall diets, lack exercise, or have other unhealthy habits that actually cause diabetes. To make the causal conclusion about sugar specifically, we need to assume that other dietary confounding factors were controlled for. Choice C provides this assumption by stating the study accounted for other dietary factors influencing diabetes risk. This isolates sugar as the causal factor. Choice A addresses other risk factors but is too narrow, focusing only on people with lower sugar intake rather than ensuring proper experimental controls throughout the study.

Question 19

1. Jordan fully disclosed to the committee every one of Jordan's personal financial holdings before last night's vote began.
2. No committee member who had a financial conflict regarding that issue failed to recuse from the vote. (correct answer)
3. Members who have financial conflicts regarding an item often do recuse themselves once another member reminds them.
4. The committee originally adopted these particular recusal bylaws by a unanimous vote of all its members.
5. The motion regarding that company ultimately passed last night by an unusually narrow and contested margin.

Explanation: The argument concludes Jordan had no conflict purely from the fact that Jordan voted. That only follows if voting guarantees no conflict—which requires that everyone who did have a conflict stayed out of the vote. The claim that no conflicted member failed to recuse supplies exactly this: if every conflicted member recused, then anyone who voted, including Jordan, must have been conflict-free. That's the sufficient assumption. Jordan disclosing all financial holdings doesn't help; someone can disclose a holding and still have a conflict, so voting wouldn't prove Jordan was clean. That conflicted members often recuse when reminded is too weak—'often' allows exceptions, so Jordan could be one. How the bylaws were adopted, unanimously or not, says nothing about whether Jordan personally was conflicted. And the margin by which the motion passed is irrelevant to Jordan's financial interest. Only one choice forces the conclusion.

Question 20

1. The express buses running next quarter will provide enough seats to carry all of the commuters being moved to those routes.
2. No commuter who switches to an express route next quarter will relocate to a home that is farther from their workplace.
3. The express buses used next quarter will not be delayed by the increased traffic that results from higher passenger volume.
4. All bus commuters are among those who, upon switching to express routes, reduce their travel times. (correct answer)
5. Commuters generally prefer riding the express buses to riding the local buses they currently take each day.

Explanation: The argument leaps from a claim about most switchers to a claim about every commuter. To make the conclusion airtight, you need an assumption guaranteeing that every single bus commuter belongs to the group whose travel time drops after switching. The choice stating that all bus commuters are among those who reduce their travel times upon switching does exactly this: it converts 'most' into 'all,' so the conclusion must follow. The seating choice only ensures everyone can board; a seat does not guarantee a shorter trip, and 'most' still is not 'all.' The relocation choice removes one reason a commute might lengthen, but it leaves untouched all the switchers who simply do not benefit. The traffic-delay choice similarly blocks one obstacle without ensuring every commuter's time falls; delays aside, some switchers may still not improve. The preference choice tells us what commuters like, but preference has no bearing on whether their commute times actually shorten. Only the choice bridging 'most' to 'all' is sufficient to force the conclusion.