Exploit the Gap in Logic on Critical Reasoning GMAT Questions

Ron Point_GMAT TipsWhen dealing with strengthen or weaken Critical Reasoning questions, it’s important to have a rough idea of what the correct answer should look like. This process is often called “predicting” the correct answer, and it helps tremendously to avoid tempting but incorrect answer choices. It’s important to note that you won’t always be able to guess the exact answer choice provided, but you can get within the ballpark. After all, the correct answer is something that will hinge on the inevitable disconnect between the conclusion stated and the evidence provided in the passage.

Let’s focus on this disconnect first. If the GMAT provided you airtight arguments that were absolutely perfect, there would be no simple way to strengthen or weaken them. As such, the arguments provided inevitably have some kind of gap in logic contained between the conclusion and the evidence that theoretically supports that conclusion. Your goal is to identify that gap and either attempt to seal it up (strengthen) or rip it apart (weaken).

Of course, a dozen different answers could all weaken the same conclusion, so it’s not always possible to predict the exact answer ahead of time. However, all the answers that weaken the conclusion stem from the same gap (not banana republic) in logic, whereby the evidence provided does not quite support the conclusion stated. If you can identify the conclusion and the gap in logic, you tend to do quite well on these types of questions.

Let’s look at an example to illustrate this point:

Researchers have recently discovered that approximately 70% of restaurant lemon wedges they studied were contaminated with harmful microorganisms such as bacteria and fungal pathogens. The researchers looked at numerous different restaurants in different regions of the country. Most of the organisms had the potential to cause infectious disease. For that reason, people should not order lemon wedges with their drinks.

Which of the following, if true, would most weaken the conclusion above?

A. The researchers could not determine why or how the microbial contamination occurred on the lemon wedges.

B. The researchers failed to investigate contamination of restaurant lime wedges by harmful microorganisms.

C. The researchers found that people who ordered the lemon wedges at restaurants were equally likely to contact the diseases caused by the discovered bacteria as were people who did not order lemon wedges.

D. Health laws require lemons to be handled with gloves or tongs, but the common practice for waiters and waitresses is to handle them with their bare hands.

E. Many factors affect the chance of an individual contracting a disease by coming into contact with bacteria that have nothing to do with lemons. These factors include things such as health and age of the individual, as well as the status of their immune system.

There is a lot of text to review for this question, so let’s begin by identifying the conclusion. (Pauses an appropriate amount of time for review). The final sentence “For that reason, people should not order lemon wedges with their drinks” is the conclusion. In fact, the first three words can be removed, as they simply point to the fact that everything previous to that sentence is evidence to back up the ultimate conclusion. The passage concludes that we should not order lemon wedges (Antilles).

Let’s examine the evidence provided to back this up: 70% of the wedges observed are contaminated, and this contamination can lead to infectious diseases. Furthermore, the study was conducted in various locations across the country. This means we can’t weaken the conclusion by simply going two towns over. Apart from that, the sky’s the limit.

At first blush, this passage seems like a classic causation/correlation problem. The majority of lemon wedges are contaminated, so we shouldn’t order the lemon wedges in order to avoid falling ill. Well what if something else (say the water) was contaminated, leading to tainted lemon wedges. Then we’d avoid the wedges without avoiding the underlying cause of the diseases. In the general sense, avoiding the lemon wedges may not have the desired effect because there is nothing guaranteeing that it is solely the wedges that cause infectious diseases.

Now let’s look at the answer choices, keeping in mind that the correct answer choice should weaken the conclusion that the wedges are somehow responsible for any potential illness.

Answer choice A, “the researchers could not determine why or how the microbial contamination occurred on the lemon wedges”, doesn’t help in any real way. Just because you don’t understand how a virus works doesn’t make it any less dangerous to you (e.g. the Walking Dead). The problem is still the lemon wedges, even if no one is sure why. This answer choice can be eliminated.

Answer choice B, “the researchers failed to investigate contamination of restaurant lime wedges by harmful microorganisms” is quite obviously out of scope. Lime wedges have very little to do with lemon wedges (despite what Sprite says), so the cleanliness of the lime wedges is irrelevant to avoiding the lemon wedges. It is possible to be tempted by this answer choice if you conflate lemon with lime, especially if you’re tired, but a thorough analysis convincingly knocks this choice out.

Answer choice C, “the researchers found that people who ordered the lemon wedges at restaurants were equally likely to contact the diseases caused by the discovered bacteria as were people who did not order lemon wedges” is spot on. We had predicted that the problem was about lemon wedges being correlated to infectious disease without necessarily causing them. This answer choice tells us that people who didn’t order the lemon wedges were exactly as likely to fall sick as those who did. Therefore, avoiding the lemon wedges (the conclusion) will have no effect on your likelihood of feeling sick. This will be the correct answer, but we should look through the remaining two choices nonetheless.

Answer choice D, “health laws require lemons to be handled with gloves or tongs, but the common practice for waiters and waitresses is to handle them with their bare hands.” is almost certainly true, but does not weaken the conclusion. Newsflash: Not everyone follows health code guidelines. (I’ve seen Ratatouille). If anything, knowing such an uncouth practice is commonplace would strengthen the idea of not ordering lemon wedges. Answer choice D is incorrect, as our goal is to weaken the conclusion.

Finally, answer choice E, “Many factors affect the chance of an individual contracting a disease by coming into contact with bacteria that have nothing to do with lemons. These factors include things such as health and age of the individual, as well as the status of their immune system” is also true, but orthogonal to the issue of lemon wedges. Perhaps you could claim that healthy people have fewer risks in ordering lemon wedges, but still it would be a health risk. This answer does not weaken the conclusion in any way, and must therefore be discarded as well.

As indicated before, your prediction might not match exactly the correct answer choice, but it will exploit the gap in logic between the conclusion and the evidence. There will inevitably be (at least) one disconnect between the conclusion and the supporting evidence presented, your goal is to identify and elaborate upon that gap. If you successfully do that on test day, you can go toast your score with a celebratory drink, lemon wedges and all.

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Ron Awad is a GMAT instructor for Veritas Prep based in Montreal, bringing you weekly advice for success on your exam.  After graduating from McGill and receiving his MBA from Concordia, Ron started teaching GMAT prep and his Veritas Prep students have given him rave reviews ever since.