Master gmat 2010 part 37 doc

The argument boils down to the following: Premise 1: If there is political instability, then the stock market is volatile unstable.. The conclusion above requires the following additiona

Example (Argument 4)

Premise: All red gremlins are spotted.

Premise: All spotted gremlins are female.

(Assumption: A gremlin must be either male or female but not both.)

Valid inference: All red gremlins are female.

Valid inference: No male gremlin is red.

Invalid inference: No gremlin that is not red is female.

Invalid inference: All female gremlins are red.

In arguments 1–4, each statement is essentially an all-or-none assertion (signaled by words

such as “all” and “no”) In this next series of arguments, the word “some” is introduced into a

premise For each form, try conjuring up your own example (perhaps involving red, spotted,

and female gremlins)

Argument 5

Premise: Some A are B.

Valid inference: Some B are A.

Invalid inference: Some A are not B.

Invalid inference: Some B are not A.

(In formal logic the word “some” means at least one and possibly as many as all; thus the

premise allows for the possibility that all A are B, and that all B are A.)

Argument 6

Premise: Some A are B.

Premise: Some B are C.

Valid inference: Some B are A.

Valid inference: Some C are B.

Invalid inference: Some A are C.

Invalid inference: Some C are A.

(If a B is an A, it is not necessarily a C as well; in other words, the set of Bs that are also As

does not necessarily overlap the set of Bs that are also Cs.)

Argument 7

Premise: Some A are B.

Premise: All B are C.

Valid inference: Some B are A.

Valid inference: Some A are C.

Valid inference: Some C are A.

Invalid inference: All C are B.

Invalid inference: All C are A.

The following two arguments involve “either-or” forms:

Argument 8

Premise: Either A or B, but not both.

Valid inference: If A, then not B.

Valid inference: If B, then not A.

Valid inference: If not B, then A.

Valid inference: If not A, then B.

Argument 9

Premise: Either A or B, but not both.

Premise: Either B or C, but not both.

Valid inference: If B, then not C (and not A).

Valid inference: If A, then C (but not B).

Valid inference: If C, then A (but not B).

A Typical Necessary Inference Question

Now that you know how to recognize various forms of deductive reasoning and distinguish between valid and invalid inferences, attempt the following GMAT-style question, which is a bit more difficult than average for this question type As you tackle the question, follow these four steps:

Try to reduce the passage to simple statements using symbols (letters) Jot down the premise and conclusion using those symbols

Before reading the answer choices, try to determine the missing premise for yourself

Scan the answer choices for your answer

For each answer choice you eliminated, try to determine what valid conclusion (if any) would be inferable by adding the premise provided in the answer choice Then read the analysis of the question and of each answer choice

In the country of Xania, periods of political instability are always accompanied by a volatile Xania stock market and by volatility of Xania’s currency compared to currencies of other countries At the present time, Xania’s currency is experiencing volatility Hence, the Xania stock market must also be experiencing volatility

8 Which of the following allows the conclusion above to be properly drawn?

(A) Whenever Xania is politically stable, the Xania currency is stable as well

(B) Whenever the Xania currency is stable, Xania is politically stable as well

(C) Whenever the Xania stock market is unstable, Xania is politically unstable

as well

(D) Whenever the Xania stock market is unstable, the Xania currency is unstable

as well

(E) Whenever the Xania stock market is stable, the Xania currency is stable

as well

The correct answer is (A) The argument boils down to the following:

Premise 1: If there is political instability, then the stock market is volatile (unstable).

Premise 2: If there is political instability, then the currency is volatile (unstable).

Premise 3: The currency is volatile (unstable).

Conclusion: The stock market is volatile (unstable).

To reveal the argument’s structure, let’s reduce it to symbols:

Premise 1: If A, then B.

Premise 2: If A, then C.

Premise 3: C.

Conclusion: B.

The conclusion above requires the following additional premise:

Premise 4: If the currency is volatile (unstable), then there is political instability.

Premise 4: If C, then A.

Only answer choice (A) provides this essential premise Note that premise number 4 above is

essentially the same proposition as answer choice (A) In other words, the following two

propositions are logically identical:

Premise 4: If C, then A.

Answer choice (A): If not A, then not C.

Choice (B) merely reiterates premise number 2 In other words, the following two statements

are essentially the same:

If X, then Y

If not Y, then not X

Choice (C) commits the following fallacy:

Premise: If X, then Y.

Conclusion: If Y, then X.

Choice (D) would lead to the conclusion that if the stock market is volatile (unstable), then the currency is volatile (unstable) In other words, (D) commits the same fallacy as (C):

Premise: If X, then Y.

Conclusion: If Y, then X.

Choice (E) merely reiterates the argument’s conclusion In other words, the following two statements are essentially the same:

If X, then Y

If not Y, then not X

Six Tips for Tackling Necessary Inference Questions

If the question asks for a missing premise, identify the premise(s) and conclusion in the passage

If you’re having trouble following the logic, reduce each part of the passage to simple statements using letters as symbols Write down the form of the argument on paper Pre-phrase the answer to the question by determining the additional premise needed for the conclusion to be valid (or the conclusion that necessarily follows from the stated premises)

Express your answer using symbols

If you’re having trouble making sense of a particular statement in the passage, try to rephrase it so its logical meaning is clearer Eliminating double-negatives can be par-ticularly helpful

Confusing: Only gremlins that are spotted are red.

Clear: All red gremlins are spotted.

Confusing: If a gremlin is not spotted, then it cannot be red.

Confusing: A gremlin is spotted only if it is red.

Clear: If a gremlin is red, then it must be spotted.

Look out for the following types of wrong answers:

• A statement that results in one of the logical fallacies identified in this chapter

• A statement that merely reiterates a stated premise (or stated conclusion), expressing it in a slightly different way

PARALLEL ARGUMENT QUESTIONS

In this type of question, the passage and the five answer choices each provide an argument (one or more premises and a conclusion) Your task is to determine which of the five choices

provides the argument most similar in its pattern of reasoning to the pattern in the passage.

Don’t expect to encounter more than one question of this type on the GMAT

You know you’re dealing with a parallel argument question when the question stem looks

similar to one of the following (notice that the first two are essentially the same, but the third

one suggests a slightly different task):

“Which of the following is most like the argument above in its logical structure?”

“Which of the following illustrates a pattern of reasoning most similar to the

pattern of reasoning in the argument above?”

“The flawed reasoning in the argument above is most similar to the reasoning in

which of the following arguments?”

A Typical Parallel Argument Question

Attempt the following GMAT-style parallel argument question, which is average in difficulty

As you tackle the question, follow these three steps:

Try to reduce the passage to simple statements using symbols (letters) Jot down

the premise and conclusion using these symbols

Perform the same task (step 1) for each answer choice

Compare the pattern of reasoning in each answer choice to the pattern in the

original passage

Then read the analysis of the question and of each answer choice

Very few software engineers have left MicroFirm Corporation to seek employment

elsewhere Thus, unless CompTech Corporation increases the salaries of its

soft-ware engineers to the same level as those of MicroFirm, these CompTech employees

are likely to leave CompTech for another employer

9 The flawed reasoning in the argument above is most similar to the reasoning in

which of the following arguments?

(A) Robert does not gamble, and he has never been penniless Therefore, if Gina

refrains from gambling she will also avoid being penniless

(B) If Dan throws a baseball directly at the window, the window pane will surely

break The window pane is not broken, so Dan has not thrown a baseball

directly at it

(C) If a piano sits in a humid room, the piano will need tuning within a week This

piano needs tuning Therefore, it must have sat in a humid room for at least a

week

(D) Diligent practice results in perfection Hence, one must practice diligently in

order to achieve perfection

(E) More expensive cars are stolen than inexpensive cars Accordingly, owners of

expensive cars should carry auto theft insurance, whereas owners of

inexpen-sive cars should not

The correct answer is (D) The original argument’s line of reasoning is essentially

as follows:

Premise: The well-paid engineers at MicroFirm do not quit their jobs.

Conclusion: If CompTech engineers are not well-paid, they will quit their jobs.

TIP

Parallel argument questions almost always involve deductive reasoning To handle these questions, you apply the forms and fallacies you just learned to the unique parallel argument format.

To reveal the argument’s logical structure, let’s express it using letters as symbols:

Premise: All As are Bs.

Conclusion: If not A, then not B.

The reasoning is fallacious (flawed), because it fails to account for other possible reasons why MicroFirm engineers have not left their jobs (Some Bs might not be As.)

Choice (D) is the only answer choice that demonstrates the same essential pattern of flawed reasoning To recognize the similarity we can rephrase the argument’s sentence structure to match the essence of the original argument:

Premise: All people who practice diligently (A) achieve perfection (B).

Conclusion: If one does not practice diligently (not A) one cannot achieve perfection

(not B)

Choice (A) reasons essentially as follows: One certain A is B Therefore, if A then B This reasoning is flawed, but in a different respect than the reasoning in the original argument Choice (B) reasons essentially as follows: If A, then B Not B Therefore, not A This reasoning

is sound (not flawed)

Choice (C) reasons essentially as follows: If A, then B Therefore, if B, then A This reasoning

is flawed, but in a different respect than the reasoning in the original argument

Choice (E) does not involve deductive reasoning and can’t easily be expressed in symbols Without additional evidence, it’s impossible to determine the strength of the argument

Four Tips for Tackling Parallel Argument Questions

Before reading the answer choices, reduce the original passage to its basic structure Express the argument in general terms—perhaps using letters as symbols—that incor-porate the argument’s logic but not its subject matter

Don’t equate logical structure with sequence The passage might provide the conclusion first, while the best answer choice provides its conclusion last (or vice-versa) In other

words, try to identify parallel logic—not parallel sequence.

Don’t equate logical structure with subject matter Be suspicious of any answer choice involving a topic that is similar to that of the passage Although that answer choice

might be the best one, more than likely it is not.

SUMMING IT UP

• Always read the question stem (or prompt) before reading the passage It will contain

useful clues about what to look for and think about as you read the passage

• Assume that all premises are factual Critical Reasoning questions are not designed to

test your real-world knowledge of passage topics Although the premises often resemble

real-world facts, whether they are factual is beside the point

• Most passages will contain a conclusion, which can appear at the beginning, in the

middle, or at the end of the passage If a passage confuses you, look for the conclusion,

then try to follow the argument’s line of reasoning from premises to conclusion.

• Read every answer choice before confirming your selection The exam directions ask you

to select the best among the five choices, and the difference between the best and

second-best choices can be subtle Unless you carefully consider all five answer choices,

you might select the second-best one without even reading the best one

• For most test takers, Critical Reasoning questions require more thought than Sentence

Correction and Reading Comprehension questions Moreover, for all but the easiest

Critical Reasoning questions, you’ll probably need to read the passage and answer choices

twice before deciding on an answer So plan to devote a bit more time to Critical

Reasoning questions than to other Verbal Ability questions

• When in doubt, go with your initial hunch about whether an answer choice is viable or

not It’s remarkably easy to overanalyze any Critical Reasoning question to the point that

you second-guess your own judgment Although you should carefully consider all five

answer choices, don’t disregard your instincts

• The 4-step plan

• Grammatical errors involving parts of speech

• Problems with a sentence’s structural elements

• Redundancy, wordiness, awkwardness, and omissions

• Errors in parts of speech

• Problems in tense, voice, and mood

• Sentence structure and sense

• Summing it up

In this chapter, you’ll do the following:

• Learn a step-by-step approach to handling any Sentence Correction question

• Learn to recognize and fix basic grammatical errors and problems with sentence structure and verbosity

• Recognize and fix challenging grammatical problems involving parts

of speech

• Distinguish between verb tenses

• Recognize and correct improper mixing and shifting of tense, voice, and mood

• Recognize and handle challenging problems involving sentence structure

THE 4-STEP PLAN

The first task in this chapter is to learn the four basic steps for handling a GMAT Sentence Correction question You’ll apply these steps to the following sample question:

1 Despite sophisticated computer models for assessing risk, such a model is

neverthe-less limited in their ability to define what risk is

(A) Despite sophisticated computer models for assessing risk, such a model is nevertheless

(B) Sophisticated computer models, which assess risk, are nevertheless

(C) Despite their sophistication, computer models for assessing risk are

(D) Assessment of risk can be achieved with sophisticated computer models, but

these models are

(E) Assessing risk with sophisticated computer models is limited because such models are

Step One: Read the Original Sentence Carefully

As you do so, ask yourself:

• Does it sound odd or wrong to my ear?

• Do any errors in grammar jump out at me?

• Is the sentence confusing, and would I have to read it again to try to figure out what

it means?

If your answer to any of these questions is “yes,” you can confidently eliminate choice (A), the original underlined part, even if you’re not sure why it’s wrong

Step Two: Plug in Your Remaining Choices

Plug your remaining choices, one at a time, into the original sentence, and read the entire

revised sentence As you do so, ask yourself the same three questions as in Step 1, and

eliminate any choice for which your answer to any of those questions is “yes.”

Step Three: If You’re Still Not Sure, Compare the Remaining Choices

If you still haven’t narrowed the choices down to a clear winner, compare the remaining candidates Resolve close judgment calls in favor of:

• A briefer, more concise version

• A version that more accurately conveys the intended meaning of the sentence

• A less awkward version

Step Four: Verify Your Selection Before Confirming Your Response

Check your selection one more time by plugging it into the sentence If it sounds right, confirm your response, and move on

Now let’s walk through the sample question about computer models, using this 4-step approach