January 12th, 2010 | 
Author: Some good cooks are gourmet cooks who pride themselves on always using extravagantly rich ingredients in elaborate recipes. Some good cooks can be characterized as fast-food cooks. They may use rich ingredients as long as the recipes are easy to follow and take little time. Other good cooks are health food enthusiasts, who are concerned primarily with the nutritional value of food. But even though not all good cooks are big eaters, they all enjoy preparing and serving food.
If the information in the passage is true, which one of the following CANNOT be true?
- Most good cooks do not use extravagantly rich ingredients.
- Everyone who enjoys preparing and serving food is a good cook.
- More good cooks who use extravagantly rich ingredients are big eaters than are good cooks who do not use such ingredients.
- There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters.
- Gourmet cooks, fast-food cooks, and cooks who are health food enthusiasts are all big eaters.
Highlight to see answer: D
Please post your explanations in the comments below!
As we’ve seen, flaw questions on the GMAT follow predictable patterns: the flaw always in some way addresses either how the evidence is being interpreted to lead to the conclusion, or how the evidence was obtained. Let’s take a look at a few specific examples of common GMAT flaws.
Real Numbers v. Percentages
At Company X, 15% of the male executives took advantage of the corporate “Family Leave” program last year, enjoying 6 weeks of paid sabbatical after a birth or adoption in their family. Only 10% of female executives at Company X took advantage of the program. Therefore, it appears that more male executives than female executives at Company X are interested in programs that promote leave options for personal reasons.
There are actually two major flaws here, and we’ll look at the one that ISN’T the title of this sub-section first, just to get it out of the way: the evidence isn’t sufficient to support the conclusion. The conclusion is about the “interest” of executives in “programs that promote leave options for personal reasons,” but the evidence only discusses percentages of executives who were involved in one specific program. Drawing a conclusion about programs in general based on that evidence is unsound. Also, participation alone is not necessarily indicative of the interest in the programs; maybe people ARE interested, but just haven’t had new babies in their families.
The more standard flaw here, though, is the “real numbers versus percentages” issue. Evidence is presented about percentages, and based on that evidence, a conclusion is drawn about quantity. But the conclusion is flawed: what if there are 100 male executives at Company X, and 200 female executives? In that case, there would be 15 male executives taking Family Leave, and 20 female executives; since 20 is clearly more than 15, the conclusion would not be properly drawn in that case. We can see, then, that percentage evidence alone is not sufficient to support a conclusion regarding “real number” quantities.
Causation v. Correlation
Studies focusing on North Americans show that single men have an average lifespan of 72.1 years; married men have an average lifespan of 73.4 years. However, married women live an average of 75.4 years, 2.1 years less than single women, who have an average lifespan of 77.5 years. Researchers have concluded, based on the data from those studies, that husbands suck the life-force out of their wives, prolonging their own lives at the cost of their spouses’ longevity.
Okay, first of all, the premise behind that scenario is absolutely a joke; just trying to bring a little levity to the GMAT preparations here! 
But seriously, the issue here is that there is a correlation between two occurrences (the increased lifespans of married men and the decreased lifespans of married women) and the argument inappropriately assumes that there must be a causal link between those occurrences. Whenever you see an argument that presents two events—let’s call them X and Y– that occur together, and that then concludes that one event, X, must be causing the other event, Y, you should look for the possibility that Y in fact causes X, or that some outside factor, Z, is causing both X and Y.
Necessary v. Sufficient
In order to successfully navigate the Great Lakes Trail, a 47-mile hiking trail fraught with unsteady terrain, one must have a pair of supportive hiking boots. Drew recently purchased a pair of the most comfortable and supportive hiking boots on the market. Therefore, Drew should have no trouble navigating the Great Lakes Trail when he goes on his hiking trip next month.
Now, I know we’ve seen a lot of necessary/sufficient issues in past discussions, but in flaw questions, the application is simpler. The correctly-identified flaw here would be that the argument takes a condition that is necessary for achieving the goal of completing the hike, and has treated it as though it is sufficient. Good boots are necessary; without them, Drew couldn’t make the hike. But are they ENOUGH? What if Drew has a horrible virus and can’t even get out of bed, let alone go for a 47-mile hike? The boots are not, by themselves, SUFFICIENT to ensure success on the hike. As a reader, be on the lookout for arguments that don’t differentiate between necessary and sufficient conditions.
Brushing your teeth regularly, no matter which toothpaste you use, will reduce your chances of tooth decay. Scientists have concluded that, when you brush, you reduce tooth decay by removing the film of plaque that forms on teeth and gums. So, you can forget about fluorides: brush your teeth carefully and say goodbye to cavities.
Which one of the following is a criticism of the reasoning in the argument?
(A) Brushing with fluoride toothpaste has been shown to reduce tooth decay.
(B) The fact that brushing will reduce tooth decay does not show that fluorides are of no value.
(C) Few people adequately remove plaque by brushing.
(D) People have plaque on their teeth most of the time.
(E) Scientists have been wrong about fluorides.
Highlight to see answer: B
Please post your explanations in the comments below!
The peculiar evil of silencing the expression of an opinion is that it robs the human race. It takes from posterity, as well as the existing generation, and from those who dissent from the opinion even more than from those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth; if it is wrong, they lose what is almost as great a benefit: the clearer perception and livelier impression of truth, produced by its collision with error.
Which one of the following best expresses the conclusion presented in the argument?
(A) Silencing the expression of an opinion is robbing the human race.
(B) Silencing the expression of an opinion harms those who dissent more than those who agree.
(C) Anyone who agrees with an opinion would not want to silence its expression.
(D) Gaining a clearer perception and livelier impression of truth is a great benefit.
(E) The greatest benefit is the opportunity of exchanging truth for error.
Highlight to see answer: A
Please post your explanations in the comments below!
Posted in Critical Reasoning | 
Tags: Critical Reasoning, gmat, gmat review, practice problems | 
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Critical Reasoning challenges logical thinking. Critical thinking items present an argument that the test taker is asked to analyze. Questions may ask test takers to draw a conclusion, to identify assumptions, or to recognize strengths or weaknesses in the argument. It presents brief statements or arguments and asks to evaluate the form or content of the statement or argument. Questions of this type ask the examinee to analyze and evaluate the reasoning in short paragraphs or passages. For some questions, all of the answer choices may conceivably be answers to the question asked. The examinee should select the best answer to the question, that is, an answer that does not require making assumptions that violate common sense standards by being implausible, redundant, irrelevant, or inconsistent.
