Flaw questions ask you to describe what is wrong with an argument’s reasoning. They are a Critical Reasoning type in the GMAT Focus Verbal section, and they are easier than they look because the GMAT reuses a small set of reasoning errors.
Learn to recognise the usual suspects. Treating a correlation as a cause. Generalising from a small or unrepresentative sample. Assuming that what is true of a whole is true of each part, or the reverse. Confusing a necessary condition with a sufficient one. Treating the absence of evidence as evidence of absence. Comparing percentages when the argument is about totals, or totals when it is about rates. Attacking a source instead of its claim.
Name the flaw in your own words before you read the choices. Then read each choice as a description of the argument and ask two questions: does the argument actually do this, and is it a mistake? Many wrong choices describe something the argument does, but that is not a flaw, or describe a flaw the argument never commits.
The answer choices are abstract, so translate them back into the argument’s specifics. “Presumes, without justification, that a condition sufficient for an outcome is required for it” becomes something concrete you can check against the text.
4 practice questions
Critical ReasoningLogical FlawMedium-hard
Question 1
A survey of 2,000 remote employees at software companies found that those who work from a dedicated home office reported, on average, 20 percent higher productivity than those who work from shared living spaces such as kitchens or living rooms. Therefore, if the software company Datavine gives each of its remote employees a stipend to set up a dedicated home office, the productivity of those employees will rise.
The reasoning in the argument is most vulnerable to criticism on the grounds that it
Arelies on a survey sample that is too small to represent remote employees at software companies
Bfails to consider that employees who have dedicated home offices may differ in other ways, such as seniority or household circumstances, that explain their higher productivity
Coverlooks the possibility that the cost of the stipends could exceed the value of any productivity gains
Dpresumes that employees who now work in shared living spaces would prefer to keep doing so
Edraws a conclusion about remote employees from evidence about employees who work in company offices
Show answer & explanation
Correct answer: B
Key Concept or Approach
The survey shows a correlation between having a dedicated office and higher productivity. The argument treats that correlation as proof that providing an office will cause higher productivity.
Step-by-Step Solution
Step 1: Identify the task (Logical Flaw) and the gap in the reasoning: The survey shows a correlation between having a dedicated office and higher productivity. The argument treats that correlation as proof that providing an office will cause higher productivity.
Step 2: (B) Correct. People who already have home offices may be more senior or have larger homes and fewer interruptions. Those factors, not the office itself, could explain the productivity gap.
Step 3: (A) A sample of 2,000 is not obviously too small, and the argument's problem lies elsewhere.
Step 4: (C) The conclusion is only that productivity will rise, not that the stipend is worthwhile, so cost is irrelevant.
Step 5: (D) The argument makes no assumption about employees' preferences.
Step 6: (E) The survey was of remote employees, so no such shift occurs.
Final Answer
Answer: B
Common trap: C is tempting because it is a sensible business objection, but the argument never claims the stipend pays for itself.
Critical ReasoningLogical FlawMedium-hard
Question 2
Historian: Of the thousands of surviving letters written by merchants in the port of Silvena during the 1600s, a large share complain about pirates, while surviving letters written by merchants in the nearby port of Carrow during the same period rarely mention pirates at all. Clearly, then, pirates attacked ships belonging to Silvena's merchants far more often than they attacked ships belonging to Carrow's merchants.
The historian's reasoning is most vulnerable to criticism on the grounds that it
Atakes for granted that how often merchants wrote about pirates reflects how often pirates attacked the merchants' ships
Bassumes that the pirates who attacked Silvena's ships were the same pirates who operated near Carrow
Cconcludes that pirate attacks caused Silvena's economic decline without offering evidence of any such decline
Ddraws a general conclusion about the merchants of two ports from the letters of only a handful of merchants
Epresumes that because pirates were active in the 1600s, they must also have been active in later centuries
Show answer & explanation
Correct answer: A
Key Concept or Approach
The evidence is about what merchants wrote; the conclusion is about what actually happened. The argument leaps from frequency of complaints to frequency of attacks without ruling out other reasons the two ports' letters differ (for example, Silvena's merchants writing to officials to seek naval protection).
Step-by-Step Solution
Step 1: Identify the task (Logical Flaw) and the gap in the reasoning: The evidence is about what merchants wrote; the conclusion is about what actually happened. The argument leaps from frequency of complaints to frequency of attacks without ruling out other reasons the two ports' letters differ (for example, Silvena's merchants writing to officials to seek naval protection).
Step 2: (A) Correct. This names the gap exactly: complaint frequency could differ for reasons unrelated to attack frequency, yet the historian treats one as a measure of the other.
Step 3: (B) The argument makes no claim about the identity of the pirates, so it does not rely on this assumption.
Step 4: (C) The historian draws no conclusion about economic decline; this describes an argument that was not made.
Step 5: (D) The passage refers to thousands of surviving letters, so the charge of relying on a handful of merchants is inaccurate.
Step 6: (E) The argument says nothing about later centuries.
Final Answer
Answer: A
Common trap: D is tempting because unrepresentative samples are a common flaw, but the passage specifies thousands of letters; the real problem is equating complaints with attacks.
Critical ReasoningLogical FlawHard
Question 3
Transportation official: Of all traffic accidents in the city of Halvern last year, only 12 percent occurred on streets that have protected bike lanes, while 88 percent occurred on streets without them. Clearly, streets with protected bike lanes are far safer for everyone who uses them than other streets are. We should therefore add protected bike lanes to as many of Halvern's streets as possible.
Which of the following most accurately describes a flaw in the official's reasoning?
AIt presumes that protected bike lanes caused the accidents that occurred on streets that have them.
BIt does not consider what share of Halvern's streets or traffic is accounted for by streets that have protected bike lanes.
CIt takes for granted that streets without protected bike lanes are used by more cyclists than streets with them.
DIt draws a conclusion about Halvern from evidence gathered in other cities.
EIt overlooks the possibility that some residents would oppose adding protected bike lanes to their streets.
Show answer & explanation
Correct answer: B
Key Concept or Approach
A share of accidents means nothing without the matching share of exposure. If only 5 percent of traffic uses streets with protected lanes, 12 percent of accidents would make those streets more dangerous, not safer.
Step-by-Step Solution
Step 1: Identify the task (Logical Flaw) and the gap in the reasoning: A share of accidents means nothing without the matching share of exposure. If only 5 percent of traffic uses streets with protected lanes, 12 percent of accidents would make those streets more dangerous, not safer.
Step 2: (B) Correct. This is the base-rate flaw. The 12 percent figure supports "safer" only if streets with lanes carry well over 12 percent of the traffic.
Step 3: (A) The official claims the lanes make streets safer, not that they cause accidents.
Step 4: (C) The argument makes no assumption about where cyclists ride.
Step 5: (D) All the data come from Halvern.
Step 6: (E) Political opposition does not bear on whether bike lanes make streets safer.
Final Answer
Answer: B
Common trap: C is tempting because it also involves usage, but the flaw is about the overall share of traffic or street mileage, not a claim about cyclist counts that the official never makes.
Critical ReasoningLogical FlawHard
Question 4
Hospital administrator: Last year, 60 percent of the patients who were readmitted to Westbrook Hospital within 30 days of being discharged had been discharged from our cardiology ward. Clearly, the cardiology ward's discharge procedures do a worse job of preventing readmissions than do the discharge procedures of the hospital's other wards, and they should be the first ones we review.
The administrator's reasoning is flawed because it
Afails to consider what proportion of all the patients discharged from Westbrook Hospital last year were discharged from the cardiology ward
Bassumes that patients who were readmitted were readmitted to the same ward from which they had been discharged
Ctreats a conclusion about one hospital's wards as though it applied to hospitals in general
Dconcludes that a procedure is ineffective merely because only a minority of the hospital's wards use it
Eoverlooks the possibility that some patients were readmitted more than once during the year
Show answer & explanation
Correct answer: A
Key Concept or Approach
The statistic is a share of readmissions, not a readmission rate. To say cardiology does worse, we need to know how its readmissions compare with the number of patients it discharges.
Step-by-Step Solution
Step 1: Identify the task (Logical Flaw) and the gap in the reasoning: The statistic is a share of readmissions, not a readmission rate. To say cardiology does worse, we need to know how its readmissions compare with the number of patients it discharges.
Step 2: (A) Correct. If, say, 70 percent of all discharges came from cardiology, then supplying 60 percent of readmissions would mean its readmission rate is actually lower than the other wards'. Without the base rate, the 60 percent figure proves nothing.
Step 3: (B) The argument is about which ward patients were discharged from; where they were readmitted is irrelevant to it.
Step 4: (C) The administrator draws a conclusion only about Westbrook's own wards.
Step 5: (D) Nothing in the argument concerns how many wards use a procedure.
Step 6: (E) Counting repeat readmissions might change the figures slightly, but the argument's core error is ignoring cardiology's share of all discharges, not double counting.
Final Answer
Answer: A
Common trap: E is tempting because repeat readmissions could distort the count, but the decisive error is comparing a share of readmissions without knowing cardiology's share of discharges.
