This is a very popular question, and the answer often elicits a sigh of relief. So, I’ll get it out of the way: yes, you can use a calculator. The GRE calculator. But using a calculator whenever you can is not always the best idea. We’ll share why mental math is just as important to your GRE prep.
Can you use a calculator on the GRE? (and more information on the GRE calculator)
First off, many problems do not require a calculator. In fact, using a calculator may very well slow you down, because you can either do the arithmetic faster in your head or on a piece of paper. The GRE calculator is on-screen, which makes it awkward to use. And it doesn’t have very many functions.
Then, there is always the case of what to calculate. While a calculator won’t make a careless error (unless you enter in the wrong number), neither will it summon the approach to a very difficult problem. Basically, the GRE math is still testing your ability to logically deconstruct a problem. In many cases, the challenge is not the math, but the approach to a problem.
When is it Advantageous to Use a Calculator?
There are times when the sum is simply too difficult to multiply on paper, and the question is not asking for an approximation. Problems such as compound interest come to mind. Perhaps you have to find the hypotenuse of a right triangle with sides of 51 and 31. Figuring out the square root of a large number could be very difficult without a calculator.
Of course, if the problem asks what is the units digit of , then you then have to come up with a clever way to approach the problem—a calculator does not hold that many digits.
Then there are those many questions that can be solved with relatively simple math. Should you go scrambling for your on-screen calculator? Or should you do the numbers in your head? For example, what if the answer requires you to multiply 150 x 8? If you’ve struggled with mental math in the past, the answer is easy: you use the calculator. But by using the awkward interface, you might make a mistake. And when the math doesn’t get you the answer but just a little bit closer to the answer, taking yourself out of the problem, by fumbling about with the calculator, might not be the best idea.
Wait, you argue. Trying to do 150 x 8 in my head is taking me out of the problem. That might be true. But that’s because you haven’t given yourself time to “exercise” your mental calculator, especially if you are always reaching for a calculator—GRE or otherwise. Learning mental math tricks and practicing mental math, the way many practice vocabulary on the GRE test, will pay huge dividends come test day. For this question, you are multiplying by 15 (forget the zero at the end of 150 for a second). 10 x 8 = 80. 5 is half of 10, so that gives you 40. 40 + 80 = 120. Add that zero (in your head of course) and you get 1200. Though it took me a few sentences to write those steps out, in your head those steps should take a mere few seconds.
The key is knowing what you can handle and what you can’t handle mathematically. Perhaps, if a problem depends on multiplying 37 x 14 you might be better off scrambling for the calculator. Though, interestingly, the math on the GRE is usually more of the 37 x 4 variety, something that is manageable.
GRE Calculator Practice
See how well you can identify those questions that you can do via mental math vs. those that require a calculator.
1. 13 x 9
2. (21+ 24+27)/3
3. 40% of 20% of 25?
4. (10 x 9 x 8)/(3 x 2 x 1)
Calculator Practice Answers
1. In your head
I know, I know. Nobody likes dealing with the number 13 (unless you’re a calculator or triskaidekaphilic). But before you scramble for the GRE on-screen calculator, think of 13 as 10 and 3. 10 x 9 = 90 and 3 x 9 = 27. Add those together (in your head) and you get 117.
2. In your head
This might look like a perfect question for a calculator, though it is anything but. Think of all the time you are going to spend punching in those twenty-somethings. Remember: The GRE math is all about pattern recognition. Notice how the three numbers on top are all divisible by 3. So we can divide each of the twenty-somethings by 3 giving us: 7 + 8 + 9, which equals 24. A quick way to this last part is noticing that 7 is one less than 8 and 9 is one more than 8. So you basically have 8 x 3.
3. In your head
What?! Is it possible? Well, when you see scary percents change them into fractions: 20% is 1/5 and 40% is 2/5 (you should know common fraction to percent and vice versa conversions). Multiplying those two fractions is easy: 1/5 x 2/5 = 2/25. When we see the word ‘of’, it means multiply: (2/25)25 is easy because we can cancel the ‘25s’, leaving us with 2.
4. It depends
If you notice that 1 x 2 x 3 = 6 and that you can divide the 9 in the numerator by this 6, you are left with 10 x 1.5 x 8. Remember, from an earlier example, that 15 x 8 = 120. Therefore, 1.5 x 8 = 12 (the decimals shaves off that zero). 12 x 10 is 120.
If you don’t see that right away, then it totally fine to use a calculator. The more you practice doing mental math on actual practice problems, the more likely you’ll pick up on these patterns. It takes time, but I’ve seen many students learn to do it with practice.
Besides a few quant wizards at Cal Tech, there are very few people who can do this in their heads. The reason is you have to multiply a number by itself 8 times. Even if that number was ‘2’ that would be relatively challenging. But we’re dealing with the relatively unwieldy decimal or 1.05. So reach for the calculator!
For shortcuts and tips on how to use the new GRE calculator to your best advantage, read our post on Calculator Strategies for the Revised GRE.
Getting a Feel for the Calculator
The best way to determine whether you will benefit from a calculator is to take a practice test using Magoosh GRE or the new GRE CD. By doing so, you should get a feel for the number and types of questions in which the calculator will help you save time, and those in which using it will only eat up time.
This frequently asked question and all others are answered in our new GRE Guide!
Editor’s Note: This post was originally published in May of 2011 and has been updated for freshness, accuracy, and comprehensiveness.
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