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Does 4x+5y = 0?

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Does 4x+5y = 0?

by bharathh » Sun Sep 06, 2009 7:23 pm
DS question from the Princeton GMAT practice test. Didn't understand the explanation. Anyone else have any ideas?

Does 4x+5y = 0?

(1) y=0
(2) 8x=-10y

OA: Answer is B. I chose D
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Source: — Data Sufficiency |
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by Bryant@VeritasPrep » Mon Sep 07, 2009 7:04 pm
the second equation alone is sufficient along with the given equation to prove that 4x + 5y = 0, since you would have two equations and two unknowns and sovling them results in a valid answer
( -5y + 5y = 0). Not only do you not need to know that y=0, y does not have to be zero to solve the two equations.
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by bharathh » Tue Sep 08, 2009 8:48 am
Thanks Bryant... but I guess I did not make my question clearer. Why is A not sufficient by itself? I can understand why B is sufficient.

If I look at the given information if y=0, x=0.. So the eqn would equal 0. Why is that insufficient?
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by alex10 » Tue Sep 08, 2009 9:26 am
A: y = 0

Therefore 4x = 0

x COULD be 0, then 4x = 0, yes. But x could be any other number as well. 2,3,12,66. 4 times 66 certainly doesn't equal 0. We don't have any information regarding the value of x. So insufficient.
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by gmat579 » Tue Sep 08, 2009 9:31 am
bharathh wrote:Thanks Bryant... but I guess I did not make my question clearer. Why is A not sufficient by itself? I can understand why B is sufficient.

If I look at the given information if y=0, x=0.. So the eqn would equal 0. Why is that insufficient?
Bharath, it looks like you assumed that 4x+5y = 0 and then solved for x when y = 0. Actually the questions asks you to for sufficiency to prove whether 4x+5y = 0.
From Stmt 1 - Given Y = 0, we still dont know the value for X and hence teh value of the equation is not known, so 1 is not sufficient.

Stmt 2 - on rearraging the equation in 2 we get 4x + 5y = 0, so sufficient.
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by bharathh » Tue Sep 08, 2009 9:35 am
Ah! Finally the tubelight flickers to life.

I get it. Thanks all!
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