MathRevolution wrote:

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Math Revolution GMAT math practice question]

Is \(xy>0\)?

\(1) x+y>0\)

\(2) |x|+|y|<1\)

Target question: Is xy>0? Statement 1: x + y > 0 This statement doesn't FEEL sufficient, so I'll TEST some values.

There are several values of x and y that satisfy statement 1. Here are two:

Case a: x = 1 and y = 1. In this case, xy = (1)(1) = 1. So, the answer to the target question is

YES, xy IS greater than 0Case b: x = 2 and y = -1. In this case, xy = (2)(-1) = -2. So, the answer to the target question is

NO, xy is NOT greater than 0Since we cannot answer the

target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of testing values when a statement doesn't feel sufficient, read my article: http://www.gmatprepnow.com/articles/dat ... lug-values Statement 2: |x| + |y| < 1Let's test values again.

Case a: x = 0.2 and y = 0.2. In this case, xy = (0.2)(0.2) = 0.04. So, the answer to the target question is

YES, xy IS greater than 0Case b: x = -0.8 and y = 0.1. In this case, xy = (-0.8)(0.1) = -0.08. So, the answer to the target question is

NO, xy is NOT greater than 0Since we cannot answer the

target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined There are still several values of x and y that satisfy BOTH statements. Here are two:

Case a: x = 0.2 and y = 0.2. In this case, xy = (0.2)(0.2) = 0.04. So, the answer to the target question is

YES, xy IS greater than 0Case b: x = 0.8 and y = -0.1. In this case, xy = (0.8)(-0.1) = -0.08. So, the answer to the target question is

NO, xy is NOT greater than 0Since we cannot answer the

target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,

Brent

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