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What is the value of (2x)/(x+y) + (3y)/(x-y) +(x^2)/(x^2 –

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What is the value of (2x)/(x+y) + (3y)/(x-y) +(x^2)/(x^2 –

by Max@Math Revolution » Mon Aug 05, 2019 12:00 am

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[GMAT math practice question]

What is the value of (2x)/(x+y) + (3y)/(x-y) +(x^2)/(x^2 - y^2)?

1) x/2 = y/3
2) x=1
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Source: — Data Sufficiency |
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by Max@Math Revolution » Wed Aug 07, 2019 1:56 am

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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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify the conditions if necessary.

(2x)/(x+y) + (3y)/(x-y) +(x^2)/(x^2 - y^2)
= (2x)(x-y)/(x+y)(x-y) + (3y)(x+y)/(x-y)(x+y) +(x^2)/(x^2 - y^2)
= (2x)(x-y)/ (x^2 - y^2) + (3y)(x+y)/ (x^2 - y^2) +(x^2)/(x^2 - y^2)
= {(2x)(x-y) + (3y)(x+y) +(x^2)}/(x^2 - y^2)
= ( 3x^2 +xy + 3y^2 )/(x^2 - y^2)

When a question asks for a ratio, if one condition includes a ratio and the other condition just gives a number, the condition including the ratio is most likely to be sufficient. This tells us that A is most likely to be the answer to this question.

Condition 1)
Rearranging x/2 = y/3 yields x = (2/3)y.
Therefore,
( 3x^2 +xy + 3y^2 )/(x^2 - y^2) = (3*(2/3)^2y^2 + (2/3)y^2 + 3y^2) / ((2/3)^2y^2 - y^2)
= ((4/3) + (2/3) + 3)y^2 / ((4/9) - 1)y^2
= 5y^2 / (-5/9)y^2
= 9
Thus, condition 1) alone is sufficient.

Condition 2) is obviously not sufficient since it provides no information about y.

Therefore, A is the answer.
Answer: A

When a question asks for a ratio, if one condition includes a ratio and the other condition just gives a number, the condition including the ratio is most likely to be sufficient. This tells us that A is most likely to be the answer to this question.
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