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.

How many cylindrical cans with a radius of 2 inches and a height of 6 inches can fit into a rectangular box?

(1) The volume of the box is 240 cubic inches.

(2) The length of the box is 3 inches.

For this question, the radius of the can is given to be 2 inches and the height is 6 inches. From condition 2, the box with length 3 inches cannot fit the cylindrical can, so the answer is 0 and (B), but the question does not come out this way.

Originally, this question has 3 variables (length, width, height) of the box, and we need 3 equations when only 2 equations are given from the conditions provided, so the answer becomes (E) as they are insufficient.

For cases where we need 3 more equation, 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.

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