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.
What is the number of cans that can be packed in a certain carton?
(1) The interior volume of this carton is 2,304 cubic inches.
(2) The exterior of each can is 6 inches high and has a diameter of 4 inches.
We have 5 variables from the original condition (2 cans (radius, height) 3 carton :length, width, height) therefore we need 5 equations. Since there is only 1 each in 1) and 2), there is high probability that E is the answer, and it turns out that E actually is the answer.
Normally for cases where we need 3 or 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 E has a high chance of being the answer (especially about 90% of 2by2 questions where there are more than 3 variables), which is why we attempt to solve the question using 1) and 2) together. Here, there is 80% chance that E is the answer, while C has 15% chance. These two are the key questions. 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 according to DS definition, we solve the question assuming E would be our answer hence using ) and 2) together. (It saves us time). Obviously there may be cases where the answer is A, B, C or D.
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