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If xy>0, is x^3y^4>0

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by Max@Math Revolution » Mon Jan 22, 2018 12:00 am
[GMAT math practice question]

$$If\ xy>0,\ is\ x^3y^4>0?$$

1) x>0
2) y>0
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Source: — Data Sufficiency |
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by Max@Math Revolution » Wed Jan 24, 2018 12:17 am
=>

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, and then recheck the question.

Modifying the question:
x^3y^4>0
= x>0
since y^4>0 is always true. We can ignore even exponents in inequalities that have 0 on one side.
So, the question becomes, 'is x>0?'.

Condition 1) is certainly sufficient.

Condition 2):
x > 0 since y > 0 and xy > 0. Thus, condition 2) is also sufficient.

Therefore, D is the answer.

Note: Tip 1) of the VA method states that D is most likely to be the answer if condition 1) gives the same information as condition 2).

Answer: D
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