Practice Set: Hard
Twenty original questions at hard difficulty. Explicitly untimed: work at your own pace. Check each answer as you go and read the explanation.
The defendant's fingerprints were on the safe, so he must have robbed it. After all, innocent people do not leave fingerprints on safes they never touched.
The reasoning is most vulnerable to criticism on the grounds that it
Prints prove contact, not burglary. The defendant may have touched the safe days earlier as a guest or worker. The argument leaps from presence to guilt.
A school district claims its phonics program improved reading, citing rising third-grade scores since adoption.
Which of the following, if true, most strengthens the district's claim?
Flat scores next door rule out a statewide trend or easier tests. The difference lines up with the program change. D names a rival cause, weakening instead.
A wine critic argues that expensive wines taste better, citing blind tastings where experts rated pricier wines higher.
Which of the following, if true, most seriously weakens the critic's argument?
If the tasters knew the prices, the test was not blind at all. Price expectations, not taste, may explain the ratings. The evidence collapses.
The city's plan to reduce emissions by subsidizing electric cars will succeed, because electric cars produce no tailpipe emissions.
The plan's success depends on the assumption that
Zero tailpipe emissions mean little if the power comes from coal plants. The net-emissions claim needs clean electricity behind it.
All of the committee's recommendations were adopted except those concerning the budget. The recommendation to hire an auditor concerned the budget.
Which of the following must be true?
Budget recommendations were "excepted" from the adopted set, but "except" does not mean "rejected": some could have been adopted separately or tabled. Nothing is forced.
The company's stock will rise. Its earnings beat expectations, and stocks of companies that beat earnings always rise.
The conclusion follows logically if which of the following is assumed?
The premise already states the universal rule; the argument is valid as written. B makes explicit that the rule truly covers this case with no exceptions.
Vera: "The dam should be removed because it blocks salmon migration, and the salmon run matters more than the dam's power." Walt: "Removing the dam would flood downstream farms during spring runoff, so the dam should stay."
Vera and Walt disagree about whether
Each gives a different reason pointing to a different action: remove vs. keep. The action is the point at issue; neither disputes the other's facts.
Most professional historians agree that the treaty was a mistake, so it must have been a mistake.
The reasoning is flawed because it
Expert agreement is evidence, not proof. Whole fields have been wrong together. Consensus deserves weight, not surrender.
A researcher claims a new teaching method improves algebra scores, based on a single classroom's gains.
Which of the following, if true, most strengthens the claim?
Random selection answers the "weird class" worry, and lasting gains answer the "crammed and forgot" worry. Two key alternatives killed at once.
The mayor claims the new park reduced crime, since crime near the park fell 20 percent after it opened.
Which of the following, if true, most weakens the mayor's claim?
Foot patrols are a direct rival cause arriving at the same time. D also weakens, but B offers a specific alternative mechanism at the exact location.
Supporters say the pipeline creates jobs, but the jobs are temporary and few. They say it brings cheap energy, but the oil is exported. Strip away the talking points and the pipeline's local benefits vanish.
The main point is that
Each claimed benefit is examined and dismissed. The conclusion is the summary judgment: the benefits vanish under scrutiny.
The critic says the novel is unrealistic because the hero survives impossible odds. But the novel is a satire, and satire exaggerates by design. Judging it by realism's standards is a category error.
The argument proceeds by
The speaker does not dispute the plot facts. It reframes the genre: exaggeration is the point of satire, so "unrealistic" misses the mark.
Every senior manager attended the retreat. Some attendees of the retreat are new hires.
Which of the following must be true?
The new-hire attendees could all be non-managers. The premises overlap at the retreat but force no overlap between the two groups.
No successful diet requires starvation. This diet requires starvation. Therefore, this diet is not successful.
Which of the following exhibits the same pattern?
Same form: No A are B, X is B, therefore X is not A. B affirms the consequent; the rest change the logic.
Banning plastic straws will meaningfully reduce ocean plastic, since straws are a visible part of beach litter.
The argument assumes that
Visibility is not quantity. If straws are a tiny fraction of ocean plastic, banning them changes almost nothing. The argument needs straws to matter by volume.
A startup claims its app reduces screen time, citing users whose weekly screen time fell after installing it.
Which of the following, if true, most strengthens the claim?
Installers who never used it are a built-in control group: same motivation to change, no treatment, no effect. That isolates the app itself.
A museum claims its new exhibit increased membership, pointing to a membership spike in the opening month.
Which of the following, if true, most weakens the claim?
A simultaneous discount is a clean rival cause for the spike. The exhibit may have contributed nothing.
The new tax policy is fair because fairness requires treating everyone the same, and the policy treats everyone the same.
The reasoning is questionable because it
The argument smuggles in a contested definition of fairness as a premise. If fairness instead means proportionality, the conclusion does not follow.
The first three speakers supported the motion. The fourth speaker opposed it. No speaker after the fourth supported it.
Which of the following must be true?
Three supporters are confirmed. Later speakers did not support it, but "did not support" is not the same as "opposed," and we do not know how many spoke. Only "at least three" is forced.
The report recommends smaller classes, more counselors, and updated textbooks. Each recommendation, however, assumes funding the district does not have. A plan without money is a fantasy.
The main point is that
The recommendations are listed only to be undercut by the funding gap. The verdict: unrealistic.
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Last updated October 12, 2026