Data Sufficiency

IF X^2+Y^2=1, is X+Y=1?
(1) Xy =0
(2) Y = 0


Im not sure about accuracy of the OA but it is C
I chose E
Your choice? and explanation plz.

G-look for ur gmat.

I don't like the question itself. The question asks for x+y. And you have the value of x+y in statement I straight away. In real GMAT, you'll never get these kinds of questions. What is the source?

papgust wrote:I don't like the question itself. The question asks for x+y. And you have the value of x+y in statement I straight away. In real GMAT, you'll never get these kinds of questions. What is the source?

I agree 100% with papgust. I think you should consider using a different resource for GMAT prep, unless this question is the exception, not the norm.

OMG.
Sorry guyz. the first condition is XY=0 but not X+Y=0
and I chose E.
sorry again.

allfta wrote:OMG.
Sorry guyz. the first condition is XY=0 but not X+Y=0
sorry again.

Might want to edit your original post ....

As for the answer,

X^2 + Y^2 = 1 (A circle with radius 1 and center 0,0)
Is X+Y = 1?

(1) XY = 0
X=0, Y=-1 => X+Y = -1
X=0, Y= 1 => X+Y = 1
Therefore, Not Sufficient alone

(2) Y = 0
=> X= +-1
=> X+Y = X = +- 1
Therefore Not sufficient alone

Options A, B and D are out
Let's see C
XY = 0 and Y = 0
=> X = +-1
Therefore, both statements TOGETHER cannot answer the question whether it is +1. It can be -1 as well.

Thus X+Y = +-1

Correct answer is E