The prices of a van and a truck were both decreased. Which vehicle had

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

The prices of a van and a truck were both decreased. Which vehicle had the greater dollar decrease in price?

(1) The price of the truck decreased by 8 percent.

(2) The price of the van decreased by 12 percent.

-> When you modify the original condition and question, this question is frequently given on GMAT math, which is “2 by 2 question” like the table below.

There are 4 variables(a, b, c, d), which should match with the number of equations. Therefore, 4 equations are needed. For 1) 1 equation, for 2) 1 equation, so we need 2 more equations. So, E is likely to be the answer. In 1) & 2), it becomes c=0.88a, d=0.92b but you cannot compare 0.12a and 0.08b. Therefore, it is not sufficient and the answer is E.

* For cases where we need 3 more equations, such as original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 80% chance that E is the answer (especially about 90% of 2 by 2 questions where there are more than 3 variables), while C has 15% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since E is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, C or D.