Have you ever finished a GMAT problem, read the explanation (or listened to your instructor give it), and thought “well how was I supposed to know ___________?!”?
If so, you’re not alone. Many test-takers become frustrated when the key to a tricky question falls outside the normal realm of math. How was I supposed to know to estimate? How was I supposed to know to flip the diagram over to notice that side AB could also be the base of this triangle? How was I supposed to know that the word “production” next to “costs” was going to be so important?
The real answer to that question, like it or not, is “you’re not”.
You’re not supposed to know those things just as a matter of course, because the GMAT is not a test of what you’re supposed to know. Geometry won’t help your financial career. Sentence Correction probably won’t help you launch a tech startup. Much of the content on the GMAT is tangential at best to the cause of becoming a captain of industry. What the GMAT is doing, in large part, is assessing whether you can recognize opportunities where others don’t, whether you can play devil’s advocate when others rush to a probable-but-not-definite conclusion, whether you can determine which details are most likely to impact the success or failure of your mission.
So while you’re not “supposed to” know the key to unlocking many of these problems, you can train yourself to spot clues on the test and then leverage those to get to the bottom of the question. Consider the example:
A girl scout was selling boxes of cookies. In a month, she sold both boxes of chocolate chip cookies ($1.25 each) and boxes of plain cookies ($0.75 each). Altogether, she sold 1585 boxes for a combined value of $1588.75. How many boxes of plain cookies did she sell?
Now, you might first look at this one and see that it has a natural algebraic setup. First, the number of plain (p) boxes plus the number of chocolate chip (c) boxes has to add to 1585, so:
p + c = 1585
Second, the price per box times the number of each boxes has to add to the total revenue:
.75p + 1.25c =1588.75
But given the size of the numbers and the decimal nature of the coefficients in the second equation, that’s not really algebra that you want to do if you can avoid it. So what clues exist to bail you out?
1) The answer choices are far apart
If the answer choices seem widely spread, as they are here (at least 90 between each choice here), there’s a good chance that you can get away with an estimate rather than an exact calculation.
2) 1585 and $1588.75 are eerily similar and close together
Because the main numbers in the problem – total revenue and total unit volume – are almost the exact same, you should see that something may be up. That means that you’re looking at almost exactly a $1.00 per box average price (a little over that), and since the average price of one of each is $1.00 (75 cents for plain, 1.25 for chocolate chip), then you’re only going to sell a hair more chocolate chip than plain but the total amounts will be just about exactly the same.
With that in mind, if you scan the answer choices, only E has a chance. An even number of each type would mean you’d sell 1585/2 of each (792.5 boxes of each), so you’re bound to sell just a little under 792 boxes of plain. And only E is anywhere near that.
Now, back to the major function of this post – you may not have immediately seen that there was a conceptual alternative to the algebra. And that may be frustrating if you spent several minutes grinding out the math (and/or giving up). The algebra is a direct blueprint for how to solve this problem, but in this case it was inefficient for many and impossible or wrought with error potential for others. So how are you supposed to know to avoid it?
It comes down to clues. The GMAT embeds clues in its problems and rewards those who finds them (more so than punishing those who don’t, actually). So part of your goal is to train yourself to recognize clues like:
-Far apart answer choices mean you may want to estimate in Problem Solving questions
-An “easy” answer of C or E on Data Sufficiency means you’re probably missing something
-The presence of a word like “all” or “only” in a CR answer choice means you need to hold that universal statement up to extra scrutiny
-A word like “its” or “and which” well outside the underlined portion of an SC question may signify that you need a singular subject or an initial “which” clause in the underline
There are plenty of clues hiding in plain sight on the GMAT, and often those clues will supersede the “tried and true mechanical” approach. Your best strategy? Keep your eyes open and be on the alert for those clues in practice, and pay attention when you recognize one so that you can find something similar in the future. And see those clues for what they are – rewards. You’ll be rewarded for seeing those clues where others don’t, so see the process of learning and searching for them as a challenge. You’re not necessarily supposed to know how to do every problem, but if you pay attention to clues you may well be able to solve them anyway.
By Brian Galvin