GRE Quantitative Comparisons Strategy
Of all the question types in the GRE, quantitative comparison questions seem to give first-time test takers the most trouble. Although these questions are in a format that may be unfamiliar to most students, there is no reason why they should be any more difficult than the standard problem-solving questions. The best way to solve these problems is to obtain clear values for both Column A and Column B. In many cases, you will be able to figure out specific numerical values for each column. In other cases, for instance when a variable is in play, you may have to settle for converting the values into similar terms.
One of the advantages of this strategy is that if you find the terms' values cannot be converted into comparable terms, you can be almost certain that the answer to the question is D (the relationship cannot be determined from the information given). Another way to simplify quantitative comparison questions is to substitute numbers in for any variables that appear in both columns. For instance, if the value in Column A is x + 8 and the value in Column B is 2x, you can try replacing the x with a few numerical values to see if the comparative value changes. It is a good idea to use a negative number, zero, and a couple of positive numbers when performing this operation. A few quick substitutions with these example values indicates that the relationships between the columns cannot be determined (after all, if x = 0, then Column A is greater, and if x = 10, then Column B is greater).