The flipside of the “strengthen” question coin on the GMAT is the “weaken” question.  The same set of evidence and conclusion can easily be used for either question type, so it’s always a good idea to start by reading the question itself first, to determine the task before you go to the argument.  After that, your approach is almost identical to the way that you would approach a strengthen question.  Take this question, for example:

Healica, a new drug that can cure a common disease that until now has been fatal for 50% of those infected, is made from the root of the New Zealand banananut tree.  The banananut tree is rare in New Zealand, and large quantities of the root are necessary in order to make Healica.  Therefore, if Healica remains in production, the banananut tree will eventually become extinct.

If true, which of the following most calls into question the conclusion above?

a) The company that holds the patent to Healica has exclusive rights to produce the drug for another 10 years.

b) Healica is expensive, and is not currently covered by most major insurance plans.

c) Banananut leaves are considered a gourmet delicacy in many parts of the world.

d) The banananut tree, although native to New Zealand, can easily be grown in other parts of the world.

e) Producing Healica is time-consuming and expensive for the drug manufacturer.

You should always read the question first, and here the commonly-used phrase “calls into question” means that this question is asking for a weakener.

Looking at the argument, we can see from the clue word “therefore” that the conclusion is the last sentence of the argument: “if Healica remains in production, the banananut tree will eventually become extinct.”  Now our job is to find a way to attack the argument, and the easiest way to do that is to identify an existing weakness and exploit it.

Here, as in many arguments on the GMAT, the argument has an unstated assumption.  The evidence states that the banananut tree is “rare in New Zealand,” and concludes that extinction will occur because of that.  But for something to be extinct, it must not exist anywhere in the world, and we only have evidence about the tree’s growth in one country.  The unstated assumptions are that the tree doesn’t grow anywhere else, and that growth can’t keep up with the demand for the trees.  A great way to weaken the argument, then, is to attack one of those assumptions.

a) The company that holds the patent to Healica has exclusive rights to produce the drug for another 10 years.

This choice would require another assumption in order to weaken the conclusion: that the one company producing Healica would not produce enough of it to kill off the banananut tree.  Weakeners, like strengtheners, shouldn’t require so much work to fit into the argument.

b) Healica is expensive, and is not currently covered by most major insurance plans.

This choice, like choice a), is not closely enough related to the argument.

c) Banananut leaves are considered a gourmet delicacy in many parts of the world.

This choice makes it more likely that the trees will be in demand and will face extinction.  The argument is strengthened, not weakened, by this choice.

d) The banananut tree, although native to New Zealand, can easily be grown in other parts of the world.

This is the correct answer, since it exploits the unstated assumptions by explicitly disproving that one of them.

e) Producing Healica is time-consuming and expensive for the drug manufacturer.

This choice has the same problem as choices a) and b): it takes extra assumptions to fit it into the argument, and that’s not what we want.

If you find yourself taking several extra logical steps to explain how an answer choice relates back to the argument and makes the conclusion less likely to follow from the evidence, then the answer choice is probably not close enough to the text of the argument as written.  Remember: stay close to the internal logic of the argument, and don’t bring in specialized outside knowledge!  The test is written so that each question belongs in its own little world, and outside knowledge is rarely relevant to finding the correct answer.

A final word on weakeners: remember that the correct answer just has to make the conclusion less likely to follow from the evidence; it doesn’t need to completely disprove the conclusion, although sometimes it will.  So make sure that you’re not looking for unnecessarily extreme answers.

One common GMAT reasoning question is the kind that asks you to “strengthen” the argument.  The most common mistake that people make on these kinds of questions is failing to stay close enough to the text of the argument as written.  Let’s look at an example:

Company X has instituted an Employee Wellness Program that will provide employees with free access to smoking cessation programs, nutritional counseling, and personal training services at a local gym.  Similar programs at other companies have been shown to improve workplace attendance and performance, and reduce the employer’s costs for employee health insurance.  Thus, the Employee Wellness Program will be good for both the employees and the company.

If true, which of the following would best support the conclusion of the argument above?

a) Many employees take advantage of free nutritional counseling when it is offered by employers.

b) Smoking cessation programs are only effective for 20% of those smokers who use them.

c) Personal training services at a local gym will make it easier for employees to improve their cardiovascular health and reduce the incidence of serious illness.

d) Exercising without personal training services can often lead to injury due to incorrect use of weight-training equipment.

e) Company X will give employees taking part in the smoking cessation program one paid hour off each Friday afternoon to participate in a support group.

Your first step here is to read the question itself, and notice that it’s asking you to find the answer choice that supports, or strengthens, the conclusion.  Then, as you read the argument, notice the word thus, which is a great clue to guide you to the argument’s conclusion, which is that “the Employee Wellness Program will be good for both the employees and the company.”  The argument’s evidence provides several examples of how to program is good for the company—it will “improve workplace attendance and performance, and reduce the employer’s costs for employee health insurance.”  But the conclusion talks about benefits for employees as well as the company, and the argument doesn’t state explicitly how the program will benefit them.  Now, let’s look at the answer choices one at a time.

a) Many employees take advantage of free nutritional counseling when it is offered by employers.

The counseling’s popularity might indicate that it is beneficial to the employees, but it might not.  This choice doesn’t clearly demonstrate that the Employee Wellness Program benefits the employees, and is a good example of a wrong answer that makes the test-taker work too hard in order to justify choosing it.  Here, one would have to assume that employees take advantage of the program because it is beneficial to them.  A strengthener shouldn’t require a major assumption, and therefore this choice is not the best answer.  Wrong answers like this are common, so watch out for them.

b) Smoking cessation programs are only effective for 20% of those smokers who use them.

This choice makes it LESS likely that the programs will benefit either the employees or the company.  This answer choice may catch your eye if you didn’t read the question closely enough, and are mistakenly looking for a weakener instead of a strengthener.

c) Personal training services at a local gym will make it easier for employees to improve their cardiovascular health and reduce the incidence of serious illness.

This is the correct answer.  The argument seems to imply that the increased attendance and performance and reduced health insurance costs are due to improved employee health, which would naturally benefit the employees.  This choice makes that unstated implication clear, and fills the gap in the argument.

If words like unstated and gap remind you of assumption questions, that’s a good thing!  Often, the weakness in an argument is due to the gap left by an unstated assumption, and the best way to strengthen the argument is by explicitly stating the assumption.

d) Exercising without personal training services can often lead to injury due to incorrect use of weight-training equipment.

This answer might be tempting, but again, it requires too many assumptions to tie it into the argument as a strengthener.  In order for this to strengthen the argument, one must assume that employees would still exercise without the personal training services, and that they would incorrectly use the weight-training equipment. That’s too much work for the question, and so this answer choice must be rejected.

e) Company X will give employees taking part in the smoking cessation program one paid hour off each Friday afternoon to participate in a support group.

This might benefit the employees, but it would be a burden to Company X.

Therefore, it’s not the best choice. Lesson of the day: one key to success with strengthen questions on the GMAT is to remember that the correct answer shouldn’t take too much work to justify.

GMAT critical reasoning questions often ask you to identify the assumption of an argument.  The first step in doing that successfully is understanding what, exactly, they mean by “assumption.”  An assumption in GMAT-speak is the unstated link somewhere in the chain of evidence and conclusion.  Finding the assumption means, basically, finding that gap in the argument and filling it.

Assumptions can be roughly divided into “necessary” and “sufficient,” and your approach to tackling an assumption question depends in part on which kind of assumption you’re dealing with.  A necessary assumption MUST be true in order for the conclusion to follow logically based on the evidence presented.  Take, for example, the following simplified version of a GMAT question:

Jennie wears glasses.  Jennie also gets A’s in chemistry.  Therefore, Jennie must be smart.

Which of the following assumptions is necessary to support the conclusion above?

Here, you’re looking at finding the unstated idea that MUST BE TRUE in order for the argument to work logically.  Take a look at the possibilities:

a) Jennie gets good grades in all of her science classes.

b) All girls named Jennie are smart.

c) Jennie wouldn’t wear glasses if she wasn’t smart.

d) Some people who get A’s in chemistry are smart.

e) Everyone who gets an A in chemistry is smart.

Now, a few of these choices support the argument’s conclusion.  But only one of them is actually necessary to the argument.  Let’s looks at them one at a time.

a) Jennie gets good grades in all of her science classes.

This isn’t an assumption of this argument at all.  Jennie’s other science classes are outside the scope of the argument, since they are addressed in neither the evidence nor the conclusion.

b) All girls named Jennie are smart.

This choice would certainly support the conclusion; if this were true, then the conclusion would HAVE to be true.  But is this statement NECESSARY to the conclusion?  No.  Other girls named Jennie don’t have any necessary significance to this argument.  So this is not a good choice.

c) Jennie wouldn’t wear glasses if she wasn’t smart.

Again, this choice would be SUFFICIENT to make the argument’s conclusion follow from the evidence.  But is it necessary?  No.  So we’ll bypass this one.

d) Some people who get A’s in chemistry are smart.

This is the correct choice, because it MUST be true in order for the evidence to follow logically from the conclusion.  What if this wasn’t true, and no one who got an A in chemistry was smart?  If that were the case, then the conclusion would not be true, based on the evidence that Jennie gets A’s in chemistry.

e) Everyone who gets an A in chemistry is smart.

Once more, this choice is sufficient to support the conclusion, but it’s not necessary.  So it’s not the correct answer to the question that is being posed.

Now, hopefully you noticed that the correct answer here is the least extreme relevant statement.  That doesn’t always have to be the case, but for questions that ask for necessary assumptions, it’s a good general guideline.  Be wary of answer choices that are extreme; they will often be sufficient, but not necessary, and will therefore trick test-takers who aren’t careful in evaluating what exactly the question has asked them to find.

But what if the question paired with that argument looked more like this?

Which of the following assumptions, if true, best supports the conclusion above?

Well, in that case, the answer choices would look more like these:

a) Jennie gets good grades in all of her science classes.

b) All girls named Jennie are smart.

c) Jennie gets A’s in her physics class.

d) Some people who get A’s in chemistry are smart.

e) Some people who don’t wear glasses are smart.

Just as in the last example, choice a) is not relevant to the argument as an assumption.  But here, choice b) is the correct answer, because if that statement is true, then the conclusion is absolutely true.  Choices c) and e) are irrelevant in the same way that choice a) is, since physics and people who don’t wear glasses aren’t at issue here.  Now, choice d) is NECESSARY to the argument, but it is not the BEST support to the conclusion.  Even if it IS true that some people who get A’s in chemistry are smart, that doesn’t guarantee that Jennie is.

Moral of the story: keep a close eye on what the question is asking for, and read accordingly.

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.

These common flaw types consistently appear on the GMAT; keep practicing on Grockit to improve your ability to spot them and improve your performance on critical reasoning questions!

Sometimes, a critical reasoning question on the Verbal section of the GMAT has an answer so clear that there’s no mistaking it.  For instance, the information given in the question has an obvious gap in it, and the test-taker quickly spots the appropriate answer and moves on.  Other times, though, the question seems bizarrely phrased, and all of the answer choices are either too extreme to be possible, or so similar to one another that choosing one comes down to a quick Eeny Meeny Miney Moe.  In those cases, the key to understanding and conquering the question is often formal logic.

Formal logic, or conditional statements, can be frustrating to the unwary test taker.  In its most basic form, a conditional statement looks like this:

If X, then Y.

See?  Not so scary, right?  But then you have to make a contrapositive of that conditional statement.  And the contrapositive of the statement above should look like this:

If not Y, then not X.

Okay.  So, you’re probably thinking that this isn’t so tricky.  And you’re right: at its simplest, formal logic is absolutely understandable.  When it gets less simple, it becomes a problem for many test takers, and I’ll talk more about that in a later blog posting.  But for now, let’s deal with X and Y—or, for clarity’s sake, a car and a key.  In order to understand how formal logic translates to our purposes on the GMAT, we need to see it at work in a real-life context.  So, here’s our car-and-key formal logic statement:

If the car starts, then the key must be in the ignition.

That makes sense, right?  The car is our X factor here—the “sufficient” factor—and the key is our Y—the “necessary” factor.  What makes one sufficient and the other necessary?  Well, the car here is sufficient because knowing that the car starts is enough information to tell us that the key must be in it.  Could the key be in it even if it didn’t start?  Sure.  If you’ve ever left your keys in the ignition and accidentally locked yourself out of the car, you’re very familiar with the fact that the car doesn’t have to be running for the key to be in the ignition.  But if the car does start, that is sufficient to tell us that the key is in the ignition.  And that’s why the car starting is the “sufficient” factor in the scenario: it’s not the ONLY thing that would indicate that the key is in the ignition, but it’s enough.  Now, let’s move on to our contrapositive:

If the key is not in the ignition, then the car doesn’t start.

So now we can see that the key is the “necessary” factor here.  If it’s not present, then the car won’t start.  Thus, we have both “necessary” and “sufficient” factors in the statement of formal logic.  But we have to be careful; if this information were part of a GMAT question, the test writers would probably try to trick us by including tempting wrong answer choices like this:

If the car doesn’t start, then the key is not in the ignition.

That looks like a contrapositive if you’re not paying close enough attention.  But we saw above that in order to form the contrapositive, the original necessary and sufficient factors had to switch places and be negated.  Here, there’s been negation, but no switch.  And looking at it logically, this statement doesn’t have to be true based on our original statement, “If the car starts, then the key must be in the ignition.”  If the car doesn’t start, yes, it could mean that the key isn’t in the ignition.  But maybe the key is in the ignition, and the car is just out of gas.  Or the battery is dead.  Or someone cut one of the little wire things under the hood like they do in movies. (Auto maintenance isn’t really my strongest area of knowledge, so I’m grasping at straws here.)  The point is, knowing that the car not starting is not sufficient to tell us whether or not the key is in the ignition.

So what can we take out of this?  Well, formal logic is tricky.  And we’ll be delving into it more later.  But for now, you as a test taker can start focusing on the necessary and the sufficient elements of statements, and using that knowledge to weed out wrong answer choices.