Critical Reasoning Skillbuilder Exit Quiz 1. Which of the following arguments exhibits a logical flaw? A) Some students have Apple laptops and all Apple laptops have Safari installed as a web browser. Therefore, some students have Safari installed as a web browser. B) All desktop computers have plug-in keyboards and some computers with plug-in keyboards are tablets. Therefore, some desktop computers are tablets. Solution: B. Note the positioning of some in choice B. All Some Conclusion is generally fraught with error, as in this case it could be that there are three types of computers with plugin keyboards (desktops, laptops, tablets) and only one of those types is part of some. B is the flawed argument. 2. Which of the following arguments exhibits a logical flaw? A) Oak trees grow only in places where it rains with some degree of regularity. It does not rain in the Sahara with any degree of regularity. Thus, oak trees do not grow in the Sahara. B) All fish swim. All whales swim. Therefore all whales are fish. Solution: B. Notice that swim could be an extremely large category of which fish and whales are two completely separate subgroups. This is why, for notation purposes, an equals sign can be tricky: Fish = Swim and Whales = Swim makes it seem like the relationship goes both ways, when really Fish and Whales are both subcategories of things that swim. For that reason, if you re going to use notation you should use an arrow to show the direction in which one group feeds into the other: Fish Swim and Whales Swim. 3. Which of the following arguments exhibits a logical flaw? A) If a letter to the editor is well-written, it will be published. Terry s letter to the editor was published, so it must have been well-written. B) If a letter to the editor is well-written, it will be published. Janet s letter to the editor is wellwritten, so it will be published. Solution: A. Here, again, note the arrow, not equals relationship. Well-written means published, but published doesn t necessarily mean well-written. It could be that the newspaper will publish anything well-written or not so while a well-written letter gets published, so does a poorly-worded one. That s still consistent with the premises but violates the conclusion in A, so A is flawed. 4. Which of the following arguments exhibits a logical flaw? A) Some scientists hypothesize that sugar is a contributing factor to a specific type of pancreatic cancer. They have found that people who consume at least 2 carbonated drinks containing sugar per day have a 90% higher rate of pancreatic cancer than those who drink the same number of
diet drinks per day. Therefore, if we were to substitute diet soda for regular soda pop, it would considerably reduce our chances of getting pancreatic cancer. B) Scientists have proven that a microbe in the drinking water in Hulett County is the sole cause of the flu-like illness sweeping through the area. The microbe can be eliminated by boiling the water before drinking. Therefore, residents of Hulett County can protect themselves from the illness by boiling their drinking water. Solution: A. The first argument makes an error of assuming causation when only correlation has been proven. Regular soda could just be one symptom of someone with a high-sugar diet, and switching from regular to diet wouldn t change the rest of the diet. It could be that the entire lifestyle is causing the cancer, and those who drink diet soda are also those who avoid sugar in other elements of their diet. So it s not the soda itself that s causing the sugar-related cancer, it s the lifestyle and soda is just one part of it. 5. From the following question stems, select the two Inference questions: A) Which of the following, if true, would most support the conclusion above? B) Which of the following can be logically deduced from the information presented above? C) Which of the following conclusions is best supported by the statements above? D) The inference above is most vulnerable to criticism on which of the following grounds? Which of the following would best help to guarantee the validity of the conclusion? Solution: B and C. A is a strengthen question, B and C are inferences, D is a weaken question, and E is a strengthen question. 6. From the following question stems, select the two Strengthen questions: A) The author s statements above support which of the following conclusions? B) Which of the following, if true, most helps to justify the city official s reasoning? C) Which of the following most calls into question the author s argument? D) Which of the following conclusions is best supported on the basis of the statements above? E) The statements in boldface play which of the following roles? Solution: A and B. A and B are both strengthen questions; C is a weaken question; D is an inference question, and E is a method question. 7. Believe it or not, dinosaurs are the ancestors of modern birds. The evidence for this surprising fact lies in the discovery of fossils that prove that many dinosaurs had feathers. Furthermore, research shows a skeletal similarity between birds and theropod dinosaurs, and suggests that this similarity is far too striking to be merely coincidental. It is expected that further research will continue to shed light on this surprising revelation.
Solution: A. Because the second sentence starts with the evidence for this, it s showing (via premise adjacent wording) that the first sentence is the conclusion and the rest of the paragraph is providing evidence for that conclusion. 8. Throughout history, economic recessions and depressions have traditionally followed periods of credit-fueled spending and speculation-induced increases in asset values. However, the axiom that those who fail to remember history are doomed to repeat it rings particularly true when it comes to the economy. The warning signs are all there but no one seems to notice. Because credit is so freely available and investors are using it to chase increasing real estate and security values, we should expect that a recession is soon to come. Solution: D. The last sentence includes the call for action we should expect, making it the conclusion. 9. Television networks are quick to cancel television shows that fail to capture a sizeable audience in their first few episodes on the air. They should not be so quick to make this decision, however, as a growing trend among viewers is to wait until the first few episodes of a show have aired and then watch them all at once. This way, viewers can develop a more instant rapport with characters and plot lines. With the advent of new technologies and distribution methods for video programming, viewers are changing the way that they consume media.
Solution: B. The second half of the second sentence provides a reason to believe the first half, making they should not be so quick the conclusion by virtue of The Why Test. 10. Companies ought to be less concerned with quarterly earnings reports and more focused on the longer-term development of sustainable business. This principle is even more important as the financial markets watch industry developments minute-by-minute instead of, as historically, quarter-by-quarter. Many companies have burdened themselves with debt or other liabilities while chasing a short-term bump in revenue that led the firm to ultimately collapse under the weight of its unwieldy obligations. Therefore, companies should always ask themselves whether the short-term strategy will continue to pay dividends in the long run. Solution: D. The fourth sentence leads with the inference trigger therefore, making it the conclusion. Instructions for questions 11-20: For each question stem, select which type of question (Strengthen, Weaken, Inference, Method) the question stem signifies. 11. Which of the following, if true, most supports the politician s claim that tax cuts will have a greater impact on the economy than will increased state spending? 12. Which of the following must be true based on the statements above? 13. Which of the following, if true, would undermine the author s conclusion? 14. The author s argument as stated above would be most vulnerable to criticism if which of the following were true? 15. The author s conclusion could not be true unless which of the following were also true? 16. Which of the following statements would serve to call in to question the author s argument that the governor s tax policy is the best course of action for the state? 17. Which of the following provides reason to doubt the author s conclusion? 18. Which of the following conclusions is best supported by the statements above? 19. Which of the following, if true, most strongly justifies the claim made by the medical doctor? 20. In her response to the board member, the chairman proceeds by
Solutions: Strengthen, Inference, Weaken, Weaken, Strengthen, Weaken, Weaken, Inference, Strengthen, Method