Assumption questions ask for something the argument needs but never states. They sit in the GMAT Focus Verbal Reasoning section with the other Critical Reasoning types, and they are the foundation for the rest: once you can see an argument’s assumption, weakening, strengthening and evaluating it become much easier.
Find the conclusion, then the evidence, then the gap between them. If the evidence talks about one group, period or measure and the conclusion about another, the author is assuming the two match. If the argument recommends a plan, it assumes nothing blocks the plan and no side effect cancels its benefit.
Most GMAT assumption questions ask for a necessary assumption, and there is a reliable test for those: the negation test. Take an answer choice, state its opposite, and ask whether the argument falls apart. If it does, the choice is required. If the argument survives, the choice may be helpful but it is not an assumption.
Wrong answers tend to be too strong or merely nice to have. “All customers prefer the new design” goes beyond what the argument needs; “some customers will notice the change” may be all it requires. Prefer the modest choice that closes the gap, and ignore choices that are true but off the conclusion’s scope.
4 practice questions
Critical ReasoningAssumptionsEasy
Question 1
Director of the Eastgate branch library: Our branch closes at 6 p.m. on weekdays, and many residents who work during the day cannot get here before then. If we extend our weekday hours until 9 p.m., the number of residents who use the branch will increase significantly. We should therefore adopt the later closing time as soon as the change can be arranged.
The director's argument assumes which of the following?
AThe cost of the longer hours can be covered by the branch's current budget.
BMost residents who now use the branch would prefer to visit in the evening.
CA significant number of working residents who cannot now use the branch would visit between 6 p.m. and 9 p.m. if it were open.
DOther branch libraries in the city are open until 9 p.m. on weekdays.
EResidents who do not work during the day visit the library more often than those who do.
Show answer & explanation
Correct answer: C
Key Concept or Approach
The director moves from "working residents can't come before 6" to "later hours will significantly increase use." That step requires that those residents would actually come in the evening.
Step-by-Step Solution
Step 1: Identify the task (Assumptions) and the gap in the reasoning: The director moves from "working residents can't come before 6" to "later hours will significantly increase use." That step requires that those residents would actually come in the evening.
Step 2: (C) Correct. Negate it: if few working residents would come in the evening, usage will not rise significantly.
Step 3: (A) The budget matters to whether the plan is feasible, but the argument's prediction is about usage, and usage does not depend on cost.
Step 4: (B) Current users' preferences are not needed. The argument is about new users.
Step 5: (D) What other branches do is irrelevant.
Step 6: (E) Comparative visit rates are not needed for the prediction.
Final Answer
Answer: C
Common trap: A is tempting because a later closing time costs money, but the argument's key prediction is about usage, which does not depend on the budget.
Critical ReasoningAssumptionsMedium
Question 2
The city of Ostrava Bay plans to reduce congestion on the Merrin Bridge by charging drivers a toll to cross it between 7 and 9 a.m. and between 4 and 6 p.m. City planners point out that many of the drivers who now cross the bridge during those hours are making trips, such as shopping trips, that could just as easily be made at other times of day. The planners therefore conclude that the toll will reduce rush-hour congestion on the bridge.
The planners' argument depends on which of the following assumptions?
AMost drivers who cross the Merrin Bridge during rush hour have no convenient alternative route.
BThe revenue raised by the toll will be spent on improving public transit in Ostrava Bay.
CCongestion on the Merrin Bridge at times of day other than rush hour will not increase once the toll is introduced.
DAt least some of the drivers whose trips could be made at other times would be deterred by the toll from crossing the bridge during rush hour.
EThe toll will be set higher than the tolls charged on other bridges in the region.
Show answer & explanation
Correct answer: D
Key Concept or Approach
The planners' evidence is that many rush-hour trips are flexible. That evidence supports the conclusion only if the toll actually moves some of those flexible trips out of rush hour.
Step-by-Step Solution
Step 1: Identify the task (Assumptions) and the gap in the reasoning: The planners' evidence is that many rush-hour trips are flexible. That evidence supports the conclusion only if the toll actually moves some of those flexible trips out of rush hour.
Step 2: (D) Correct. Negate it: if no flexible driver is deterred by the toll, the fact that their trips could be made at other times gives no reason to expect less rush-hour traffic, and the argument collapses.
Step 3: (A) The argument does not need this. If drivers had alternative routes, the toll could reduce bridge traffic even more easily.
Step 4: (B) How the revenue is spent has no bearing on whether the toll reduces rush-hour congestion.
Step 5: (C) The conclusion concerns rush-hour congestion only. Traffic moving to other times is exactly how the plan is supposed to work, so more off-peak congestion would not undermine the conclusion.
Step 6: (E) The toll only has to be high enough to change some drivers' behavior; it need not exceed tolls elsewhere.
Final Answer
Answer: D
Common trap: C is tempting because shifted trips would add traffic at other times, but the conclusion is only about rush hour, so off-peak congestion rising does not hurt the argument.
Critical ReasoningAssumptionsMedium-hard
Question 3
Chief financial officer of Veltrix Pharmaceuticals: "Cutting the price of our Aeris asthma inhaler by 40 percent will increase our total revenue from Aeris. At the new price, Aeris will be the least expensive inhaler of its type on the market, and pharmacy data show that most patients whose insurance co-payments vary with a product's price switch to the least expensive equivalent product."
The chief financial officer's argument depends on which of the following assumptions?
AA significant proportion of patients who use inhalers of Aeris's type have insurance under which their co-payments vary with the product's price.
BVeltrix's cost of producing each Aeris inhaler will not rise as the number of inhalers it produces increases.
CMost patients who currently use Aeris are satisfied with how well it controls their asthma.
DAeris is more effective at controlling asthma than any competing inhaler of its type.
ENo competing inhaler of Aeris's type is currently sold at a price lower than Aeris's current price.
Show answer & explanation
Correct answer: A
Key Concept or Approach
The evidence covers only patients whose co-payments depend on price. For the price cut to raise revenue through switching, enough patients must fall into that group.
Step-by-Step Solution
Step 1: Identify the task (Assumptions) and the gap in the reasoning: The evidence covers only patients whose co-payments depend on price. For the price cut to raise revenue through switching, enough patients must fall into that group.
Step 2: (A) Correct. Negate it: if few patients have price-linked co-payments, few will switch, and a 40 percent price cut with little extra volume lowers revenue.
Step 3: (B) Production cost affects profit, not revenue, and the conclusion is about revenue.
Step 4: (C) The argument relies on new patients switching to Aeris, not on current users' satisfaction.
Step 5: (D) The argument relies on price, not on Aeris being the most effective inhaler.
Step 6: (E) Cheaper competitors may exist today. The claim is only that Aeris will be cheapest after the cut.
Final Answer
Answer: A
Common trap: B is tempting because it sounds like a business prerequisite, but it concerns costs and profit, while the conclusion is only about revenue.
Critical ReasoningAssumptionsVery hard
Question 4
Researchers at Helix Labs have developed a blood test that detects pancreatic cancer with 95 percent accuracy. Helix argues that testing every adult over 50 once a year would substantially reduce deaths from the disease. Pancreatic cancer, Helix notes, is almost always fatal when diagnosed at the late stage at which it is usually discovered today, but in most cases it can be cured if treated at an early stage.
Helix's argument relies on which of the following assumptions?
AMost adults over 50 would agree to be tested every year if the test were offered to them.
BFew patients would be harmed by follow-up procedures prompted by false-positive test results.
CThe test can detect the disease in a substantial proportion of cases while it is still at an early stage.
DPancreatic cancer is more common among adults over 50 than among younger adults.
ENo other test currently available detects pancreatic cancer with an accuracy as high as 95 percent.
Show answer & explanation
Correct answer: C
Key Concept or Approach
Screening saves lives here only by catching the cancer early, while it can still be cured. The 95 percent figure does not say at what stage the test detects the disease.
Step-by-Step Solution
Step 1: Identify the task (Assumptions) and the gap in the reasoning: Screening saves lives here only by catching the cancer early, while it can still be cured. The 95 percent figure does not say at what stage the test detects the disease.
Step 2: (C) Correct. Negate it: if the test mostly detects the disease only once it is advanced, screening finds tumors that are already fatal and deaths do not fall. The argument collapses.
Step 3: (A) Negate it: even if only 40 percent agreed, annual testing of those who did could still substantially reduce deaths. Not required.
Step 4: (B) Harm from false positives bears on overall costs and benefits. The argument is only about reducing deaths from this cancer.
Step 5: (D) The argument does not need the over-50 group to be at higher risk. It needs screening that group to reduce deaths.
Step 6: (E) Whether a rival test exists does not affect whether this test would reduce deaths.
Final Answer
Answer: C
Common trap: A feels necessary because screening needs participants, but a large minority taking part could still cut deaths substantially, so the negation does not destroy the argument.
