simple one

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allfta: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Tue Jun 08, 2010 2:45 am

by allfta » Sun Jun 20, 2010 1:10 am

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.

Last edited by allfta on Sun Jun 20, 2010 8:12 pm, edited 2 times in total.

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Source: Beat The GMAT — Data Sufficiency | Sun Jun 20, 2010 1:10 am

papgust: Community Manager; Posts: 1537; Joined: Mon Aug 10, 2009 6:10 pmFollowed by: 252 members; Thanked: 653 times

by papgust » Sun Jun 20, 2010 7:25 am

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?

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Patrick_GMATFix: GMAT Instructor; Posts: 1052; Joined: Fri May 21, 2010 1:30 amFollowed by: 98 members; Thanked: 335 times

by Patrick_GMATFix » Sun Jun 20, 2010 10:23 am

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.

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allfta: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Tue Jun 08, 2010 2:45 am

by allfta » Sun Jun 20, 2010 6:26 pm

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

Last edited by allfta on Sun Jun 20, 2010 8:13 pm, edited 1 time in total.

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aagar2003: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Tue Sep 08, 2009 8:46 pm; Thanked: 1 times

by aagar2003 » Sun Jun 20, 2010 7:59 pm

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

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