How to Solve a Puzzling GMAT Critical Reasoning Problem:

by on April 12th, 2018

Yes or No
Most Critical Reasoning problems on the GMAT involve arguments. We might be asked about the argument’s structure, how to strengthen or weaken the argument, how to evaluate it, or sometimes what key assumption the author is making in their argument. Those are what I would consider the bread-and-butter GMAT Critical Reasoning question types.

But once in a while, you’ll get a Critical Reasoning question that doesn’t ask you to do any of that. Sometimes the questions are basically just riddles.
So here’s a classic riddle to get us started. It shares some key features with the GMAT question type we’ll be examining in a moment.

A father and his son are driving in the car and get in a terrible car accident. Tragically, the father is killed instantly. The son survives, but is seriously injured and is rushed to the nearest hospital for emergency surgery. As the boy is wheeled into the operating room, the surgeon looks down at the boy and says, “I can’t operate on this boy; he’s my son.” How is this possible?

Take a minute.

If you’re stumped, I’ll tell you this: it’s not a trick question. This isn’t one of those annoying “lateral thinking exercises” that hinges on using language in an intentionally misleading way. The man who was killed isn’t somebody else who was in the car with them, or a priest that I’m referring to as “father,” and he’s not a ghost or anything.

Still stumped? You’re going to kick yourself when I tell you. Okay, here goes.

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The surgeon is the boy’s mother.

(That’s the classic answer, but to be fair, it’s not the only valid answer to this riddle. Step-parents or adoptive parents would work, too. When I pose this riddle to my students in class, I sometimes get the response “it’s his other dad” before I get the “it’s his mom” response. All are perfectly logical, and I think it says something interesting about how much progress our society has made in some areas relative to others.)

Now, the GMAT isn’t going to ask you a riddle about gender roles or implicit social biases—the writers don’t want to touch any of that with a ten-foot pole—but they absolutely will ask you questions that have a similar structure to the riddle we just saw.

We call them Explain the Discrepancy problems. Basically, they tell you a story, and at some point in the story, there’s a twist: something happens that’s the opposite of what we would expect based on the setup. But it’s not really a twist. There’s something else going on that will make everything we’ve been told perfectly logical and harmonious. In a sense, we’re being asked to untwist the twist.

Let’s try a real one from GMATPrep*. Put 2 minutes on the clock and give it a go.

Many small roads do not have painted markings along their edges. Clear edge markings would make it easier for drivers to see upcoming curves and to judge the car’s position on the road, particularly when visibility is poor, and would therefore seem to be a useful contribution to road safety. However, after Greatwater County painted edge markings on all its narrow, winding roads, the annual accident rate along those roads actually increased slightly.

Which of the following, if true, most helps to explain the increase in accident rate?

A. Greatwater County has an unusually high proportion of narrow, winding roads.

B. In bad weather it can be nearly as difficult for drivers to see the road as it is at night.

C. Prior to the painting of the edge markings, Greatwater County’s narrow, winding roads already had a somewhat higher accident rate than other Greatwater County roads.

D. Many of the accidents on narrow, winding roads involve a single vehicle veering off the road, rather than the collision of two vehicles.

E. After the markings were painted on the roads, many drivers who had gone out of their way to avoid driving on those roads at night no longer did so.

Okay, let’s break it down.

Step 1: Identify the question type. Anytime you see “helps to explain” or words like “surprising” or “puzzling” in the question stem, then you know it’s an Explain the Discrepancy question.

Step 2: Deconstruct the argument. In this question type, there isn’t a conclusion based on premises—just some facts and then an apparent twist. Our goal at this step is to find the twist. The county installed some new safety features on their narrow, winding roads, so we would expect that to make the roads safer. Except that then the accident rate actually went up on those roads! What’s up with that?

Step 3: State the goal. We’re looking for something that will untwist this twist—something that will explain why the roads with new safety features somehow became more likely to be the sites of car accidents. Try to brainstorm some ideas before you go to the answers: Maybe the safety features were poorly-designed and backfired in some weird way, causing more drivers to crash? Or poorly-installed?

Step 4: Work from wrong to right. Go down the line and eliminate anything that definitely isn’t the answer. If something seems potentially interesting, we’ll hold onto it for now and then do a second pass.

A. Greatwater County has an unusually high proportion of narrow, winding roads.

The fact that the county has a lot of these narrow, winding roads doesn’t tell me anything about why the safety features did the opposite of what we expected. Eliminate.

B. In bad weather it can be nearly as difficult for drivers to see the road as it is at night.

Obviously, that’s true, but I don’t see how it explains anything. Maybe if the county had particularly bad weather that year, that could have contributed to causing more accidents, but that’s not what they’re saying. Eliminate.

C. Prior to the painting of the edge markings, Greatwater County’s narrow, winding roads already had a somewhat higher accident rate than other Greatwater County roads.

This is sort of interesting. They’re saying these narrow, winding roads were already more accident-prone than other roads in the county. So maybe there’s something special about these roads that would make the safety features not work right. Let’s hold onto this.

D. Many of the accidents on narrow, winding roads involve a single vehicle veering off the road, rather than the collision of two vehicles.

Go back and double-check the original argument—they never mentioned anything about specifically single-car accidents vs. two-car accidents. Also, the edge markings are specifically designed to help prevent single cars from losing track of the edge and veering off the road, so if anything, this makes the situation even more puzzling. Eliminate. (Answer choices that do the opposite of what we want are common wrong answers in Strengthen, Weaken, and Explain the Discrepancy questions.)

E. After the markings were painted on the roads, many drivers who had gone out of their way to avoid driving on those roads at night no longer did so.

So before the markings were installed, these drivers (and there are “many” of them) were actively avoiding driving on these roads at night, but after the markings were installed, the drivers thought they could handle it. That seems like a recipe for trouble. If the new safety features caused these (possibly not very skilled) drivers to become overconfident in their ability to safely handle the narrow, twisting roads, then that could certainly lead to more accidents.

Quickly go back and double-check C, though. The original argument only mentions that the markings were installed on the “narrow, winding roads,” and the accident rate that went up unexpectedly is also specific to those same roads. So comparing these roads to other wide, straight roads in the county doesn’t affect or explain anything. C’s out.

The answer is definitely E.

*GMATPrep questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

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