Key Strategies for GRE – Quantitative Comparison Questions

On the GRE, the Quantitative Comparison questions ask you to compare two numeric quantities—Quantity A and Quantity B.

Based on the information given, you have to choose one of the four options: (A) Quantity A is greater than Quantity B, (B) Quantity B is greater than Quantity A, (C) The two quantities are equal, and (D) The relationship between the two quantities cannot be determined from the information given.

Let us look at a few points that any experienced online GRE tutor would communicate to help you approach these questions:

1. The answer options are always the same

The answer options in the Quantitative Comparison (QC) questions are always the same, as listed above. So, it helps if you can memorize the order of the answer options. This will save you a lot of time as you won’t have to refer to the instructions every time you attempt a GRE Quantitative Comparison question.

If you observe that the two quantities A and B are based on mathematical computation of any form, the answer can never be the last option, i.e., option D, no matter how complicated the computations may seem. The best way to proceed in the case of complicated calculations is by cancelling common terms from both quantities A and B, if present, and making approximations to simplify calculations.

If two quantities are in variable form, where the variables are real numbers, an optimum approach is to plug-in the variables with a few test numbers to determine the comparison. For example, if you have a "modulus" term, it is best to try it with a positive set of numbers and then with a negative set of numbers. If there are numbers with exponents in the quantities, try with a set of numbers greater than 1 in magnitude and then with another set of numbers with a magnitude of between 0 and 1. Remember that squared (or even-powered) numbers are always non-negative.

   4. Always, Sometimes, or Never

Remember that GRE QC questions represent "always true" types of questions. Thus, if you find that in all cases, except one, Quantity A is greater than Quantity B, and that in only one case, Quantity B is greater than Quantity A, the answer must be option D: "The relationship between the two quantities cannot be determined." Thus, if you observe that, in a few test cases, one quantity is greater than the other, but you are not sure whether it is true for every case, try to analyze logically if any exceptions can come up. In general, QC questions on the GRE won’t be too complicated; thus, if one quantity is greater than the other, in most cases, that remains the correct comparison. Let us look at an example to understand this point.

A QC question:

                                      (–m)(|m|) > 0

Quantity A                             Quantity B

                                                                   m³                                                          1/m

(–m)(|m|) > 0 is the information given and taking this information as fact, we have to compare Quantity A (m³) and Quantity B (1/m).

Since (–m)(|m|) > 0, we can deduce that (m)(|m|) < 0. Since |m| is always non-negative, we can conclude that m < 0 or m is negative.

To compare the quantities A and B, let us plug-in the test values for m once with numbers between 0 and –1 and once with numbers less than –1.

• For 0 to –1: If m = –1/2, then m³ = –1/8, while 1/m = –2, implying quantity A (–1/8) is greater than quantity B (–1/2).

• For less than –1: If m = –2, then m³ = –8, while 1/m = –1/2, implying quantity B (–1/2) is greater than quantity A (–8).

Since we do not get a unique answer, the relationship between the two quantities cannot be determined; thus, the answer is option D.

   5. Don't judge a geometry problem by its figure

For GRE quantitative comparison geometry-based questions, remember that the diagrams provided are not necessarily drawn to scale. So, taking dimensions or estimating angle values from the diagram is a very bad idea. Memorize the rules of geometry of triangles: isosceles, equilateral, and scalene triangles; the Pythagorean theorem; triangle inequality; and similarity of triangles. Remember that triangles are the building blocks of plane geometry, so if you are stuck at some point, try breaking the diagram into triangles to simplify the question.

breaking the diagram into triangles to simplify the question.

Note that GRE QC is not about simply solving math problems; many QC questions can be solved with the application of logic. Applying the above strategies can help in cutting down on the time taken to solve QC questions. Remember to use logic wherever necessary; mathematics and logic always go hand in hand.

Working with a GRE coach is often the most efficient way to learn how to best approach GRE quantitative comparison question. If you are considering a GRE tutor, contact us today and we’ll offer a free GRE diagnostic session.