CP #10

GMAT Blue Quiz - Kaplan

UNDERSTAND EXPLANATION!!!

Question

Is a – b > 0?

(1)    a > 2b

(2)    b > a + 3

Solution

The inequality in the question stem can be manipulated so that the question reads "is a > b?"

At first glance, Statement (1) would seem to be sufficient. If a and b are both positive, and then a is certainly greater than b. But what if a and b are negative? If a = -3 and b = -2? Since -3 > -4, a would be greater than 2b; but since -2 > -3, b would be greater than a. Since Statement (1) can lead to either a yes or no answer, it is insufficient.

Manipulating the inequality in Statement (2) is more fruitful. Subtracting b and 3 from both sides gives you -3 > a-b. If that's true, then a – b is certainly less than zero. Statement (2) leads to a single, definite answer (which happens to be "no") and so is sufficient.