GRE Quantitative Comparison

Every Quantitative Comparison question has the same four answers: Quantity A is greater, Quantity B is greater, they are equal, or the relationship cannot be determined. About a third of Quant questions use this format.

Choose D only with two cases

The answer is D when two values allowed by the information give different results. So test cases on purpose: a positive whole number, zero, a negative number and a fraction between 0 and 1, whichever the conditions allow.

Example. $x$ is not zero. Quantity A: $x^2$. Quantity B: $x$. With $x = 2$, A is greater; with $x = \tfrac12$, B is greater. The answer is D.

Simplify before you calculate

Do the same thing to both quantities until they are easy to compare. Quantity A: $3^{20} + 3^{20} + 3^{20}$. Quantity B: $3^{21}$. Three copies of $3^{20}$ make $3^{21}$, so they are equal: C, with no arithmetic.

When D is impossible

If both quantities are fixed numbers, the answer can never be D.

Free lesson: Quantitative Comparison