GRE Sample Test 5 Quantitative Reasoning 1

First, isolate each variable. 2a < 6 → a < 3. 3b > 27 → b > 9. Now, assume that a = 3 and b = 9. In this case, b − a = 9 − 3 = 6. Since a < 3 and b > 9, the difference between the two must be greater than 6. Thus, 6 is not a possible value for b − a.