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In the figure, lines AB, CD and EF are parallel, and lines B

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In the figure, lines AB, CD and EF are parallel, and lines B

by Max@Math Revolution » Tue Jul 23, 2019 12:34 am

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[GMAT math practice question]

In the figure, lines AB, CD and EF are parallel, and lines BC and DE are parallel. What is the length of CD?

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1) AB=3
2) EF=12
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Source: — Data Sufficiency |
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by Max@Math Revolution » Thu Jul 25, 2019 12:11 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 conditions if necessary.

Triangles ABC and CDE are similar, and triangles BDC and DFE are similar. So, we can set up the proportion AB:CD = CD:EF.
Since CD^2 = AB*EF, conditions 1) and 2) together give us sufficient information to calculate the value of CD.

Therefore, C is the answer.
Answer: C
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