With the advent of the calculator on the GRE, some would say the days of knowing how to do mental math are obsolete. While you could rely on the calculator for the entire test, doing so may actually slow you down. Indeed a facility mental math will save you a lot of time, and may help you avoid any careless slip of the fingers.

## Focus on the problem

Momentarily stepping out of the problem, so to speak, to attend to the calculator can interrupt the flow. You may forget exactly what the number pertained to. Was it the answer? Or was it one of many calculations you need to do to arrive at the answer? If it is the latter, then you may forget your place and have to start over.

## Speed

By constantly relying on the calculator you can get a case of calculator-itis. Even easy computations has you running for the on-screen calculator. While you may be fast with your fingers, being able to calculations like 14 x 5 in your head will be a lot of faster. And with so many such calculations, those few seconds per calculation adds up to quite a lot over the course of the test.

## Slippery fingers

Sure, we are all prone to mental math mistakes. But we are also prone to entering in the wrong numbers, especially under timed conditions. If it is a simple calculation, sharpen your calculator brain—don’t let 17 x 3 = 42, because of a simple slip of your finger.

## The power of approximation

Some questions may seem daunting, but with just a little mental approximation you can quickly get the answer. What is 15% of 50,200? Well, it’s a little bit greater than 7,500. If only one answer is close to 7,500 then you save yourself the time of having to enter the number into the calculator.

You may balk thinking that you’d prefer the accuracy, but remember working out your mental math muscle before the test will help you become far more adept at doing quick calculations in your head.

## Takeaway

Using a calculator makes sense when you are dealing with big numbers, especially in the case of data input. But if you are dealing with smaller sums (say 20 x 12), then relying on math can save you a lot of time. And you won’t have to worry about any slippery fingers.

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Aside from the practice and use of mental math making evident better and more efficient solutions for the preparing for the exam, is not using a calculator and doing it in your head actually faster when it comes to test day? It takes on average 3-7 seconds to make a calculation on a calculator. Are you saying that mental math will be faster than that? And are you also saying that saving at most 3 seconds per calculation (saving at most four minutes on the entire quant section) is that important? This of course means that in using mental math you will spend no more than 4 seconds for any given calculation. People who can do this for anything beyond memorized advance times tables are close to, or actually hold world records, for their ability to do rapid mental math. I can spend 30 seconds trying think through 56/780. I can probably shave that down to ten if I write it on paper, but there’s no way I could do that in under 4 seconds in my brain.

Hi Jack,

Great question! As you mentioned, mental math is a great tool to use in order to gain a deeper understanding of how numbers relate to each other and how to solve difficult math questions more efficiently. However, you are absolutely right that sometimes it just makes more sense to use the calculator! Basically, each individual must create his own calculator strategy using his strengths and weaknesses as a guide.

Here’s the basic rule of thumb: It’s fine to use the calculator when you think it will get you the answer faster. Now what exactly does that mean? Well, that means something a little bit different for each student. Some students are really good at mental math and can do pretty much everything quickly on their own. For other students, that’s going to be more challenging and time-consuming.If it’s faster for you to punch 56/780 into a calculator, then that may be the best course of action! Keep in mind, however, that the answer choice might be presented in a fraction form instead of with decimals, so solving this on a calculator could actually cause more work! It’s also surprisingly easy to make a simple calculator mistake, and the test-makers account for common calculator mistakes in the wrong answer choices. So sometimes the fastest way to solve part of a question (using the calculator) isn’t actually the most efficient method.

My best advice is to build your mental math muscles as much as possible before the exam. Sometimes, it will make more sense to use the calculator, and you should definitely do this when it makes sense! But there will be many other times that you are grateful for the quick calculation power that mental math allows you to do. As you continue to practice, you should find your own personal calculator strategy that works best for you 🙂

Do you know any good apps for android that will allow me to practice my mental math?

Hi Sarah,

You can play sudoku.

Very helpful. Thanks a ton Chris!

You are plenty welcome 🙂

Hi Chris,

I have an unrelated question to ask you. I recently got my hands on this huge GRE book that contains “27 previously administered full-length tests.” The problem is that it’s from 1998. Although the questions won’t be in the Revised GRE format, can I still use the the problems for practicing?

Thanks,

Gaia

P.S. Magoosh is AMAZING. Thank you thank you thank you!

Really helpful post, Thanks Chris!

PS – I think you inadvertently added another zero at the end of 7500. =)

So much for my mental math :).