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Problems solving equation from a DS problem

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Joined: 07 Feb 2009
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Problems solving equation from a DS problem [#permalink] New post 30 Oct 2010, 10:04
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A
B
C
D
E

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0% (00:00) correct 100% (01:24) wrong based on 5 sessions
Hi,

Question: What is the value of x+3y+7?
(1) X - 3Y = 0
(2) X^2 + 4Y^2=0
1 KUDOS received
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Joined: 24 Jun 2008
Posts: 978
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Kudos [?]: 725 [1] , given: 3

Re: Problems solving equation from a DS problem [#permalink] New post 30 Oct 2010, 11:42
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vivaslluis wrote:
Hi,

Question: What is the value of x+3y+7?
(1) X - 3Y = 0
(2) X^2 + 4Y^2=0


Statement 1 is not sufficient, since while we can work out that x = 3y, which means we're trying to work out the value of 6y + 7, we don't have any information about the value of y. It might be that x = y = 0, in which case x + 3y + 7 = 7, or it might be that x = 3 and y = 1, in which case x + 3y + 7 = 13, among many other possibilities.

From Statement 2, since x^2 and y^2 are both squares, they can never be negative; each must be at least zero. The only way for x^2 + 4y^2 = 0 to be true then is if x^2 and y^2 are both zero, in which case x = 0 and y = 0. So Statement 2 is sufficient, and the answer is B.
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Intern
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Joined: 07 Feb 2009
Posts: 14
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Kudos [?]: 12 [0], given: 13

Re: Problems solving equation from a DS problem [#permalink] New post 30 Oct 2010, 15:37
Thank you Ian.
IMO the right answer was E but I found out OA = B. However I didn't have any explanation why it was B and not E.

Thanks again
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Re: Problems solving equation from a DS problem [#permalink] New post 30 Oct 2010, 17:10
vivaslluis wrote:
Hi,

Question: What is the value of x+3y+7?
(1) X - 3Y = 0
(2) X^2 + 4Y^2=0


I think it's B because X^2 + 4Y^2=0 only when X = 0 and Y = 0.
Therefore x+3y+7 = 7
Re: Problems solving equation from a DS problem   [#permalink] 30 Oct 2010, 17:10
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