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Calculator Strategies for the Revised GRE

For many students, the addition of the GRE’s onscreen calculator to the revised exam is a godsend. These students take solace in the notion that this new calculator will help them solve tons of questions. The truth of the matter is that almost all math questions on the revised GRE can be solved without a calculator. Furthermore, in many cases, it will actually take long to solve a question using a calculator that it will to use other techniques. Finally, the test-makers are taking questions that can be easily solved with a calculator and changing the numbers in order to render the calculator useless.

For example, a former GRE question would have asked you to evaluate {203^2} – {201^2}. The slow solution was to perform the actual (tedious) calculations. The fast solution was to recognize that this difference of squares can be factored as (203+201)(203-201), which equals (404)(2), which equals 808.

Since this question would be too easy to solve using the onscreen calculator, the test-makers will change the question to 20003^2- 20001^2 where 20003^2 and 20001^2have too many digits for the calculator to handle. As such, you’ll have to solve this question using factoring techniques.

Aside: the onscreen calculator displays up to eight digits. If a computation results in a number greater than 99999999 then an ERROR message is displayed. When you evaluate 20,003^2 you get a 9-digit number.

Now, despite the test-makers’ attempts to remove the calculator from your arsenal, there are times when you can make a few adjustments to a question and then quickly answer it with the calculator.

Now, in my last post, we solved the following question using a variety of techniques and strategies:


Column AColumn B


  1. The quantity in Column A is greater
  2. The quantity in Column B is greater
  3. The two quantities are equal
  4. The relationship cannot be determined from the information given


Notice that these numbers yield products that are too big for the calculator to handle. However, with a few adjustments we can use a new strategy with the calculator to answer the question.

One solution is to first divide each column by 1,000,000. When we do this, we get:

Column AColumn B

From here, we can rewrite this as:

Column AColumn B

And this is the same as:

Column AColumn B

At this point, we can use the calculator enter all of these values, and each resulting product will have fewer than 8 digits.

So, with a small modification, we can answer this question using a calculator.


Now, can you think of another approach that allows you to use a calculator to solve the original question (without dividing by 1,000,000 or any other powers of 10)?

Here’s the original question:

Column AColumn B

Another approach is to first divide both sides by 641,713 to get:

Column AColumn B

Then, divide both sides by 897,189 to get:

Column AColumn B

At this point, we can enter all of these values into the calculator and compare the columns.


Next, we’ll examine another strategy to thwart the revised GRE and use the onscreen calculator to solve questions that, at first glance, appear to render the calculator useless:

The square root of 2 billion is between

  1. 2,000 and 5,000
  2. 5,000 and 15,000
  3. 15,000 and 30,000
  4. 30,000 and 50,000
  5. 50,000 and 90,000

Try to identify at least two ways to solve the above question.

Aside: Please notice that 2 billion is too large to fit in the onscreen calculator.


Non-calculator strategy:

This approach uses the following rule: 

sqrt{ab} = sqrt{a}sqrt{b}

First we need to recognize that:

sqrt{2 billion} =  sqrt{2,000,000,000}



=sqrt{20} * 10,000

From here, we can see that since sqrt{16}=4 and sqrt{25}=5 then sqrt{20} must lie between 4 and 5. In other words, we can say that sqrt{20} equals 4.something.

If  sqrt{20} equals 4.something, then = sqrt{20} * 10,000 must lie between 40,000 and 50,000.

As such the answer must be D.


Calculator strategy:

With a slight modification, we can use the onscreen calculator to solve the question within seconds.

First recognize that:

sqrt{2 billion} =  sqrt{2,000,000,000}



From here we can use the calculator to evaluate both roots. When we do this, we get:

sqrt{2,000}sqrt{1,000,000} = 44.7 * 1,000 = 44,700

So, the answer must be D.

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8 Responses to Calculator Strategies for the Revised GRE

  1. Niladri Saha October 11, 2017 at 11:27 pm #

    641713*451222 is greater here..please validate the answer

  2. Eric November 2, 2014 at 10:52 pm #

    For the first one, I prefer the solution given in the Magoosh videos: if I use a calculator, 64×45=2880. 90×32=2880. Since the actual numbers of A are a bit bigger, and the actual numbers of B are a bit smaller (rounded up), then A must be bigger. Simple, fast. 😉

  3. Bhavesh July 25, 2014 at 7:45 am #

    This is one of the import skill to save critical time.


    • Chris Lele
      Chris Lele July 28, 2014 at 11:33 am #

      Glad it was helpful! Anything that helps save time–without sacrificing accuracy–is a good thing 🙂

  4. Vanan December 9, 2011 at 7:36 pm #

    Hi Brent,
    Your tips are really awesome and Magoosh is really doing a great job publishing excellent tips for the students to ace GRE.. Hats off Magoosh!!!


  5. Praveen December 9, 2011 at 10:19 am #

    Hello Sir,

    thanks for the simple and useful tips! they make u think.. “that was so obvious y didn’t i think that at the first place! “.

    Magoosh is the only site which offers so many articles with invaluable tips for free! Keep up the good work 🙂


    • Brent
      Brent December 9, 2011 at 12:06 pm #

      Hi Praveen,

      Thanks for the feedback!


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