Is xy = 1?

[VJesus12]

Is xy = 1?

(1) x > 1
(2) y^2 = x

The OA is the option C.

I don't know how could I prove that xy=1 using both statements. May someone helps me? Please.

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Hi VJesus12,

We're asked if (X)(Y) = 1. This is a YES/NO question and we can answer it by TESTing VALUES.

1) X > 1

Fact 1 tells us that X is greater than 1, but tells us nothing about the value of Y.
IF.....
X=2, Y=2 then the answer to the question is NO
X=2, Y=1/2 then the answer to the question is YES
Fact 1 is INSUFFICIENT.

2) Y^2 = X

IF.....
X=4, Y=2 then the answer to the question is NO
X=1, Y=1 then the answer to the question is YES
Fact 2 is INSUFFICIENT.

Combined, we know...
X > 1
Y^2 = X
Since X > 1, we know that Y will either be greater than 1 OR less than -1. Thus, there is NO way for (X)(Y) to equal 1 and the answer to the question is ALWAYS NO.
Combined, SUFFICIENT

Final Answer: C

GMAT assassins aren't born, they're made,
Rich