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How to use your calculator on the GRE

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When the 2011 revision of the GRE added a calculator to the test's array of onscreen tools, many test takers were thrilled. But the GRE calculator function is hardly the equivalent of taking a T-89 with you into the testing center. It's cumbersome to use and does very little (four functions with square roots and those cryptic memory options few of us ever master). So how should you use the GRE's onscreen calculator?

As little as possible

My wife hates GPS devices. She thinks they take a driver's focus off the road and weaken his ability to use judgment and navigate by landmarks. I'm not such a purist behind the wheel but the analogy holds for calculator use. Over-reliance on a calculator takes your focus away from the questions and the clues embedded therein. Remember that the GRE is a reasoning test and not an achievement test of one's math ability. Therefore, you are meant, more often than not, to think your way through problems.

The area of a rectangular flower garden is 400 square feet. If the dimensions are tripled, what will the new area be?

In a problem like this, it's tempting to choose a set of numbers for the dimensions of the garden, triple each and then multiply to get a solution. However, this calculate-first approach glosses right over the simpler solution. The factor by which you increase the dimensions of a figure will be squared when you calculate the area (and cubed when you calculate volume). So tripling the dimensions of the garden will increase the area of the garden nine-fold. So all we need do is multiply 400 X 9 to get 3600--a calculation easily done by hand.

For calculations that you can't do quickly in your head or on paper

Even though the GRE added the calculator function a few years back, the test makers didn't make the calculations any more onerous. The test is still written in such a way that you could do all questions within the time constraints with nothing more than your brain, pencil and paper. Numbers are often chosen for easy solving. For example, when multiplying an integer by a fraction, you'll nearly always find that the denominator of the fraction divides evenly into the integer, reducing the problem to simple division followed by multiplication. I implore all of my students to study their times tables and to remember the approximate value of common fractions like 1/5 (0.2) or the square root of 2 and 3 (1.4 and 1.7). Use real-life shortcuts as well. For instance, instead of solving 175/25 on a calculator, ask yourself how many quarters are in $1.75. How long will it take to drive 135 miles at 70 miles per hour? Well 60 miles per hour is a mile a minute, so 135 miles at 70 mph should take less than 135 minutes or around two hours.

At the end of the problem

The ideal place to perform a calculation is after you have broken down the question and set up the calculations that you're going to perform. If all that's left to do is a little number crunching and the calculation is neither quick nor obvious by hand, then it's OK to use the calculator. Consider the following problem:

After a 35% decrease, the value of a home is $97,500. What was the original value?

In a problem like this, you should first set up an equation: 97,500 = X - 0.35X = 0.65X. To solve you then divide 97,500 by 0.65. I could do this by hand if I wanted to and so could you, but who wants to? Doing it on a calculator reveals the answer, $150,000, in about five seconds. If you want to check your work, you can multiply 150,000 by 0.65 in five seconds as well. Situations like these are just about the only times when I will use a calculator on the GRE.

Rich Carriero has been a standardized test prep teacher and tutor since 1999. In addition to his position as Academic Manager for Next Step Test Preparation’s GRE tutor and GMAT tutor programs, he is also a freelance writer.