How to Start a Critical Reasoning Question

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There is a debate in the LSAT and GMAT communities about where to start a critical reasoning question (the LSAT calls them logical reasoning, but everything I say holds true for both). One camp holds that you should start by reading the paragraph of information (usually an argument). The other says that you should start by reading the question before doubling back to read the argument. I’m amazed the argument even exists.

Imagine if they released the “Where’s Waldo?” books without a title. Here’s a massive jumble of people. That’s nice. After you’ve spent a couple minutes looking at the page, someone tells you that you are supposed to be looking for Waldo. Sure, there’s a chance you stumbled upon Waldo when you were looking at everything else, but there’s a much greater chance that you spent your time focusing on a whole lot of other irrelevant things.

Read the question first. It allows you to focus on the correct things and to figure out what’s important and what isn’t. And that’s even more relevant because not all critical reasoning questions ask about the same thing. Some tell you that an argument is coming and ask you to figure out what would strengthen it. Some tell you an argument is coming and ask you to find a flaw. Some tell you there’s no argument, just a set of facts and ask you to find what must be true. Knowing which of the question types you’re going to get allows to focus on the proper approach to the problem, filter out the irrelevant information and find Waldo much more effectively.

 Checking All of the Boxes

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The GRE is a multiple choice test whose purpose of late seems to have been defeating decades of conventions in multiple choice strategy. With the relatively recent revisions to the test, the makers of the GRE have created a system where simply being able to estimate or get rid of wrong answers often isn’t good enough to get the job done. However, that doesn’t mean there aren’t smart approaches to the new GRE.

Today we’ll consider the question type where you are asked to select one or more answer choices that satisfy the conditions set forth in the problem. So, if you’re given 7 choices, only one may be correct, or all of the the answers may be correct. You will only be given credit for the problem if you select all of the correct answers and none of the incorrect answers. Here’s an example:

Which of the following is greater than 0.33?

Select ALL such answers:

A) 3/13

B)  1/4

C) 2/7

D) 5/16

E) 3/8

F) 2/5

G) 7/17

GRE answer choices are typically listed in either ascending or descending order. This is not simply a trivial fact, but rather something you should use to your advantage. When you look at this list of numbers you’ll encounter several unfamiliar ones. If you can’t come up with the decimal equivalents of these numbers off the top of your head, you’ll be forced to either do the long division or punch all of these numbers in your calculator. That’s not a terribly tough process, but it can be a time-consuming one. However, since these numbers are listed in ascending order we can use that to our advantage.

First look at choice B, 1/4. We know that 1/4 is one quarter, which has a decimal equivalent of 0.25, so it is a wrong answer. We also know that since the answers are in ascending order, choice A must be incorrect as well. Moving down toward the bottom we find 2/5, which should also be easy to convent to a decimal, this time 0.4. Since that is greater than 0.33 we know that choice F is part of the correct answer and also that choice G is part of the correct answer since the answers are ascending.

This leaves only the middle three choices to work through in order to find that dividing line between choices less than 0.33 and choices greater than that amount. Keep this example in mind when working through practice problems so that you can use the order of the answer choices to your advantage.

 Strategy Sunday: Skipping Questions

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There are many advantages to being able to take the GMAT on the computer. You get a much truer sense of your abilities because the computer can be adaptive while a paper test cannot. You eliminate the risk of smudged ink making a geometry question impossible to decipher. You get the flexibility to take the test almost any time that’s convenient for you without the test-makers having to worry about questions “getting out”. But it does make timing more challenging.

 

Unlike a paper-based test where you’re free to skip a difficult question so that you can come back and work on it later, once you’ve skipped a question on the computer-based GMAT it’s gone, never to be seen again. Well, maybe you’ll see it in those haunting dreams you have the night after the test. Because, you see, the vast majority of the questions you face are going to be things that you could answer… if you had enough time. The task being asked of you is not so much what can you do, but rather what can you do in 75 minutes.

 

The computer-adaptive nature of the test can seem cruel to test-takers of any ability. Whether you’re scoring in the 400s or the 700s there are going to be math questions that are at the limit of your abilities. If you continue to answer questions correctly, you’re eventually going to get to those questions. And that’s where the dilemma comes in: do you spend some extra time to get that really tough question, or do you take a guess and move on?

 

With few exceptions, the correct tactical decision is to guess and move on. Questions at the beginning of the test are no more important than the ones at the end of your test, and if you’re sacrificing the time you need to answer two questions correctly at the end in order to answer one question in the middle of your test, you’re losing that trade. Plus, even if you do manage to get that very difficult question correct, your reward will be an even tougher question! Go through this cycle a few more times and you’re faced with questions that are certainly beyond your reach and a time deficit that will be nearly impossible to overcome.

 

Take this strategy to heart: set time markers. Make sure you’re finished with 10 questions with 55 minutes to go. Make sure you’re finished with 20 questions with 35 minutes to go. Make sure you’re finished with 30 questions with 15 minutes to go. Hitting these markers might require making a quick guess on number 9 or taking a complete shot in the dark on number 20, but it’s worth it. The GMAT penalizes you heavily for failing to answer the last question(s) so it’s likely that any good you do yourself early in the test will be more than offset later.

 

Keep those time markers in mind. If you get a little ahead, you know you have some freedom to take an extra minute on that tough question. If you fall behind, take quick measures to get yourself back into a good position. Even if you realize after the test that the question you skipped and took a wild guess on was one you could have answered, if you follow this advice you’ll be too happy celebrating a great score to worry too much about that!

 Variable Approaches

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Marlo travels 17 yards every x seconds.  How many seconds will it take him to travel y yards at the same speed?

 

A student I was working with encountered a very similar problem to this one and proceeded to make a mess of it. I took a look at his algebra, and slowly tried to figure out where the error had entered the equation. It took a full minute of careful searching to find the error, and even when I explained what had gone wrong all I got was a blank expression in return.

 

Completing this problem algebraically starts with two equal rates (where z is the variable we’re trying to solve for in number of seconds):

 

17/x = y/z

 

Multiplying both sides by z:

 

17z/x=y

 

Multiplying both sides by x:

 

17z =xy

 

And dividing both sides by 17:

 

Z=xy/17

 

The real challenge here is in getting the initial equation set up correctly, because the manipulations from there are pretty straightforward. But, rather than give an in-depth algebra lesson to my student, my question was why? Why even mess with the algebra? Why go down a path so fraught with peril if you know that algebra isn’t a huge strength of yours? The part of this problem that I haven’t given you, and the part that makes all the difference is the answer choices.

 

A)    17xy

B)    17x/y

C)    17/xy

D)    x/17y

E)     xy/17

 

Since we’re given variables in the answer choices, rather than deal with them and their potential for confusion, let’s instead plug our own values in for x and y, figure out the answer and then see what matches.

 

For instance, let’s say Marlo travels 17 yards every 5 seconds. We’ve now defined that x=5. If y=34 yards, we can easily calculate that it will take Marlo 10 seconds to travel that distance at the same speed. So, when we pick x=5 and y=34, the answer should be 10. Let’s test the answer choices to find what’s consistent with our choice.

 

A) 17xy ; 17(5)(34) = Way more than 10, not correct

B)    17x/y ; 17(5)/(34) = 2.5, too small. Eliminate this one.

C)    17/xy ; 17/(5)(34) = Much smaller than 10, move on.

D)    x/17y ; (5)/(17)(34) = Much too small again

E)     xy/17 ; (5)(34)/17 = 10. There we go!

 

There are no hero points for taking on complicated algebra equations on a multiple choice test. Let this example show you that when you have variables in your answer choices picking numbers is a great strategy to get you to the correct answer… whether your math teacher would have done it that way or not!