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Understanding GRE Quantitative Comparison Questions


In this article, we’ll work through a standard GMAT sentence correction question that involves comparisons using an Official Guide to the GMAT diagnostic exam practice problem. You can either read this article or watch this GMAT sentence correction video on YouTube.

GRE Quantitative Comparison Practice Question

1)           Quantity A                                     Quantity B

     The least prime number                      The greatest prime number

     greater than 24                                    less than 28

  1. A) Quantity A is greater
  2. B) Quantity B is greater
  3. C) The two quantities are equal
  4. D) The relationship cannot be determined from the information given

As is the case with every GRE strategy, the first step is to set up your scratch pad.

As you scan the potential answers to a quantitative comparison problem, the first thing you're going to want to do is to write out the question number and the two quantities on your scratch paper. Note that the quantities themselves are the most important information. 

In this case, we can shorthand quantity A as the “least prime # >24.” For Quantity B, we're looking at the “greatest prime #<28.”

To aid the process of elimination, we'll place our four answer choices in between our two quantities. Until you’ve 100% memorized the four options, you can use helper symbols to remember what each answer choice is referring to. With this in mind, you can place a greater than symbol facing Quantity A above choice A, a greater than symbol facing quantity B above choice B, an equal sign above choice C, and “N/A” above choice D.

Now that your scratch pad is set up, it’s time to look at the problem.

Whenever you're approaching a quantitative comparison question, your first step is to decide whether or not you need to plug in. In this case, however, we don't have any variables. Instead, we're dealing with arithmetic definitions for quantity A and quantity B. 

Since there are no variables in the quantitative comparison, we can immediately eliminate choice D. The reason for this is that we can be certain that there is a least prime number greater than 24, and that there is a greatest prime number less than 28. As we move forward, remember that a prime number is an integer greater than zero with exactly two factors. 

As we’ve already seen, quantity A refers to the “least prime number greater than 24.” Upon closer inspection, it becomes evident that 25, 26, 27, and 28 are not prime numbers. 


As soon as we hit 28, then, it becomes clear that no matter what, the correct answer is A.

We hope this example, explained by one of our expert GRE tutors, was helpful. To learn more about our online GRE tutoring, visit us here. Learn more about our perspective on tutoring, how we help you identify strengths, weaknesses, build a customized study plan, explain difficult concepts, and more here. Happy studying.

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