Solved Examples for Critical Reasoning

Q1: The enormous distances between stars are not spaces entirely devoid of matter. The interstellar spaces are filled with "dust": very low-density matter. This minuscule amount of matter, spread over almost infinite distances, acts like a curtain obscuring the stars that lie behind. If it were not for this material, we would see no dark patches in the sky at night: the sky would be entirely covered with stars. 
The two parts in boldface play what roles in the argument above?
(a) The first is a suggestion that the author wishes to dispute. The second is a hypothesis that the author wishes to explain.
(b) The first is the main point the author wishes to make. The second is a hypothetical result of accepting that point.
(c) The first is a fact that the author thinks is important in explaining a certain phenomenon. The second is a result that the author would expect if that fact were not true.
(d) The first is a speculation that the author wishes to justify. The second is a consequence that would result if that speculation is not true.
(e) The first is an established fact that the author wishes to explain. The second is a consequence of accepting this fact.
Ans: (c)
Explanation: The first bold sentence states a factual claim about interstellar space containing dust; it is presented as a matter of fact rather than an opinion or a claim to be disputed. The second bold sentence describes what we would expect to observe if that fact were absent - namely, an entirely star-covered sky. Thus the first functions as an explanatory fact and the second as the expected result if that fact were not true. Options (a) and (d) are wrong because the author does not treat the first statement as a suggestion or speculation to be challenged. Option (b) is incorrect because the second sentence is not a premise that follows from acceptance of the first; rather it is a counterfactual consequence. Option (e) is incorrect because the second is not presented as a consequence of accepting the fact but as what would occur if the fact were false.

Q2: In a recent study of responses to visual images, researchers found that women most frequently gave the rating "most attractive" to images of male faces that were more feminine in contour, and rated more masculine faces, on average, "less attractive." The researchers concluded that modern women prefer men who are less obviously masculine in their facial features.
The conclusion would be most severely weakened if which of the following were true?
(a) Facial features are not the criterion that most women use to decide whether a man is attractive.
(b) The visual images were computer-generated composites of photographs and not pictures of actual men.
(c) The rating scale was a ten-point scale with most attractive scoring 1-2 and least attractive scoring 8-10.
(d) Most popular male actors have the features that the study allocated to the more masculine category.
(e) The faces with the more masculine features were all significantly older than those with the feminine features.
Ans: (e)
Explanation: The researchers infer a preference for less masculine facial features from the ratings, so their conclusion relies on the assumption that masculinity of facial contour is the relevant factor driving attractiveness ratings. If all the masculine-featured faces were significantly older, then age - not facial masculinity - could be the reason for lower attractiveness ratings. That would create a confounding variable and thus severely weaken the conclusion. Options (a) and (b) weaken the study to an extent but do not most severely undermine the specific link between facial masculinity and preference; (c) merely describes the scale and does not directly undercut the causal inference; (d) is irrelevant to the internal validity of the experiment. Therefore (e) is the best choice.

Q3:In a recent study of responses to visual images, researchers found that women most frequently gave the rating "most attractive" to images of male faces that were more feminine in contour, and rated more masculine faces, on average, "less attractive." The researchers concluded that modern women prefer men who are less obviously masculine in their facial features.
Which of the following is an assumption that the researchers apparently made in this study?
(a) The women who participated in the study were sufficiently representative of modern women in general.
(b) Male faces are, in general, attractive to women.
(c) Visual images are important to women.
(d) It is impossible to predict what features an ideal face would have.
(e) Women in previous ages would have preferred more masculine men.
Ans: (a)
Explanation: The conclusion is framed about "modern women" generally, so the researchers must be assuming that their sample of female participants represents modern women as a whole. Without representativeness, the generalisation to all modern women would not be justified. Options (b), (c), (d) and (e) are either irrelevant to the logical step from sample to generalisation or make historical claims not required by the study's conclusion. Hence (a) is the necessary assumption.

Q4: Photography is no longer an art form. Nowadays everyone has access to digital cameras that only need to be pointed at the subject in order to generate a perfect image.
The writer of the argument apparently assumes that
(a) the selection of the subject is not an important artistic factor in photography
(b) digital cameras will continue to improve in quality
(c) digital cameras can never go wrong
(d) photography with all other types of camera is an art form
(e) art is not perfect
Ans: (a)
Explanation: The argument claims that photography is not an art because anyone can "point and shoot" to get a perfect image. For this to support the conclusion, the writer must assume that choosing what to photograph (the subject) does not itself require artistic skill. If subject selection were important, then photography could still be an art despite automated image capture, and the conclusion would fail. Options (b) and (c) are unnecessary suppositions about camera technology rather than the argument's core assumption. Option (d) is stronger than needed and not implied, and (e) is unrelated. Therefore (a) is the assumption the writer relies upon.

Q5: Red is a color which has powerful effects on human beings as well as animals. A group of psychologists carried out an experiment which confirms the subconscious effects of this color on human behavior. They provided selected sports teams at school and college level with either red or blue shorts and recorded the outcome of the games. The teams wearing red won in a disproportionate number of matches. The psychologists suggested that either the teams wearing red subconsciously felt themselves more powerful, or that the non-red teams were subconsciously intimidated by the red color.
Which of the following, if true, would most weaken the psychologists' suggestion?
(a) Each team wore red in some matches and blue in others.
(b) The color blue has the subconscious effect of making human beings less competitive.
(c) The effect was only observed if all the team members wore white shirts.
(d) Red signifies danger in some cultures whereas it signifies happiness in others.
(e) In a subsequent study, teams with all-red outfits were more likely to report that they thought they would win no matter what color the opponents wore.
Ans: (b)
Explanation: The psychologists attribute the teams' higher win rate to the positive effects of red. However, if blue itself causes reduced competitiveness, then the difference in outcomes could be due to a negative effect of blue rather than a positive effect of red. This alternative explanation confounds the causal claim that red increases performance, thereby most strongly weakening the psychologists' suggestion. Option (a) actually strengthens internal control and does not weaken the suggestion as much. Option (c) points to a conditional effect but not the key confound; (d) is about cultural interpretation and is less directly relevant to the experimental result; (e) supports the psychologists' suggestion rather than weakens it.

Q6: The number of people diagnosed with dengue fever (which is contracted from the bite of an infected mosquito) in North India this year is twice the number diagnosed last year. The authorities have concluded that measures to control the mosquito population have failed in this region.
All of the following, if true, would cast doubt on the authorities' conclusion except
(a) more cases are now reported because of increases in administrative efficiency
(b) a very high proportion of the cases were in people who had recently returned from neighboring countries
(c) an effective diagnostic test was introduced about nine months ago
(d) the disease is prevalent only in some industrialized areas which have shown a dramatic increase in population due to migration
(e) the incidence (number of cases per thousand) of malaria, also contracted from mosquito bites, has increased
Ans: (e)
Explanation: The authorities infer that mosquito-control measures have failed because dengue cases doubled. Options (a)-(d) each offer alternative explanations that could explain the increase without implicating failed control measures - better reporting (a), importation of cases (b), improved diagnostics (c), and population increases in affected areas (d). Option (e), however, reports that malaria incidence (also mosquito-borne) has increased; this finding is consistent with a real rise in mosquito populations and therefore does not cast doubt on the conclusion that control measures failed. Thus (e) is the exception.

Q7: Sue: Commercial flights currently contribute more carbon dioxide to the atmosphere in one year than does the whole of Africa. If we want to reduce global warming we need to restrict the number of flights we take.
Dave: Did you know that by taking one inter-continental flight you cause more pollution than you would in twelve months of car travel?
Dave's response to Sue's comment serves to
(a) reinforce Sue's contention that flights are a major contributor to increased carbon dioxide levels
(b) add more weight to her contention that we should reduce the number of flights we take
(c) mitigate the force of her argument by suggesting that there is an alternative approach
(d) suggest an alternative that will reduce the effect of pollution
(e) question whether she really understands the severity of global warming
Ans: (b)
Explanation: Dave's statistic about pollution from a single inter-continental flight supports Sue's general claim that flights contribute substantially to pollution. Although he does not mention carbon dioxide specifically, his point provides additional evidence that flying is highly polluting and therefore bolsters the recommendation to reduce flights. It does not introduce an alternative method (so (c) and (d) are incorrect), nor does it challenge Sue's understanding (so (e) is incorrect). Option (a) is close, but (b) is more precise because Dave's remark strengthens the practical recommendation to cut flights.

Q8: It is not unusual to see the ball fall into a black slot on a roulette wheel four times in a row. But for it to fall five or six times in a row into the same color is very unusual. Therefore you can win money by waiting for a run of five of the same color and then betting against that color.
If the roulette wheel in question is a fair wheel, which of the following observations or facts, if it were true, would best reveal a fallacy in the logic?
(a) If there were a reliable way to win at roulette, it would be well-known by now.
(b) It is hard for a player to keep track of what went before for the time required.
(c) The probability of getting a particular color decreases with the number of times the color has appeared.
(d) The probability of getting a particular color is always the same no matter what has gone before.
(e) A person who makes money this way once or twice, will carry on to lose that money after a few more times.
Ans: (d)
Explanation: The argument exemplifies the gambler's fallacy - the mistaken belief that past independent events affect the probabilities of future independent events. For a fair roulette wheel each spin is independent, so the probability of a given colour remains constant regardless of previous outcomes. Statement (d) exposes this fallacy directly. Option (c) states the false idea that would support the argument rather than reveal its error. Options (a), (b) and (e) are peripheral remarks about practicality or long-term loss but do not pinpoint the logical mistake as clearly as (d).

Q9: On the basis of the Big Bang theory scientists predicted levels of Helium-3 in the universe that are ten times greater than the levels actually observed. According to the original model, Helium-3 is produced when low-mass stars burn up hydrogen and become 'red giants', as well as being produced in the Big Bang itself. Researchers have now produced a new model in which the Helium-3 produced by a red giant is pushed to the star's interior and burnt up. Hence the Big Bang theory is no longer undermined by Helium-3 data.
The two portions in bold-face are related to each other in which of the following ways?
(a) The first highlights an observation that tends to undermine a particular theory. The second is that theory.
(b) The first is a fact that undermines a theory. The second is context for accepting that theory.
(c) The first points to an inconsistency in a particular model; the second is the author's main conclusion.
(d) The first is a challenge to a classic theory; the second resolves that challenge.
(e) The first is a position that the author does not accept; the second is the author's position.
Ans: (c)
Explanation: The first bold portion states a factual prediction-observation mismatch - predicted Helium-3 levels exceed observed levels - which indicates an inconsistency in the existing model. The second bold portion expresses the author's conclusion that, with the revised stellar model (which burns up Helium-3 internally), the mismatch is resolved and the Big Bang theory is no longer undermined. Thus the first identifies the inconsistency and the second gives the main conclusion reached after introducing the new model. Options (a), (b) and (d) are close but either mislabel the roles or do not capture that the second is the author's primary conclusion derived from resolving the inconsistency; (e) is incorrect because the author does accept the initial factual claim.

Q10: The committee on sexual discrimination in the workplace has highlighted Supremo Company as a chief offender. Of the twenty senior executives in the firm, only one is a woman. And of the forty junior executives, only five are female. Supremo could best defend itself against the charges by showing that
(a) male and female executives at the same level have the same qualifications
(b) they pay the same salary to senior men and senior women
(c) ten times more men than women apply for jobs with the company
(d) the work pressures and long hours make jobs with the company unattractive to married women
(e) all job applicants who were rejected had fewer qualifications than those accepted
Ans: (e)
Explanation: To rebut a charge of sex discrimination in hiring or promotion, the firm must show that decisions were made on objective merit rather than on sex. If Supremo can demonstrate that every rejected applicant - irrespective of sex - had fewer qualifications than the successful applicants, this supports the claim that selection was based on qualifications and not discriminatory bias. Option (a) is relevant but narrower; (b) concerns pay rather than hiring or promotion decisions; (c) and (d) offer explanations that could be asserted but would be weaker legal or logical defences than direct evidence that selection was strictly merit-based. Therefore (e) is the best way for Supremo to defend itself.