gmatbusters wrote:
Project DS Butler: Day 56: Data Sufficiency (DS111)
For DS butler Questions Click HereIf x = 2y, what is the value of xy ?
(1) x > Y
(2) 3x - 2y = 14
Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.
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Since we have 2 variables (x and y) and 1 equation, D is most likely to be the answer. So, we should consider each condition on its own first.
Condition 1)
If x = 2, y = 1, then we have xy = 2.
If x = 4, y = 2, then we have xy = 8.
Since condition 1) does not yield a unique solution, it is not sufficient
Condition 2)
We have 3x - 2y = 3x - x = 2x = 14 or x = 4, y = 2 since x = 2y.
Since condition 2) yields a unique solution, it is sufficient
Therefore, B is the answer.
If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E.
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