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If x=0.5, is y = 1? GMATPrep Quant DS

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zarak_khan
 Post subject: If x=0.5, is y = 1? GMATPrep Quant DS
 Post Posted: Sat May 15, 2010 3:38 am 
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Course Students


Posts: 25
If x = 0.5, is y =1?

1) (y^2)*(x+0.5) = 1
2) y*(2x-1) = 2x-1

OA = E

My solution is as follows:

Statement 1---> y^2 = 1 ---> y = + or - 1 Insufficient
Statement 2---> y*(2x-1) = 2x-1
Here, we cannot simply divide the right-hand side of the equation with 2x-1. Why is this so? I guessed at the answer, thinking GMAT would not test simple arithmetic and got the right answer, but I am not very clear on the logic behind this solution.

I have tried searching for a post on this problem but not found any.

Thanks!
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mkim1213
 Post subject: Re: If x=0.5, is y = 1? GMATPrep Quant DS
 Post Posted: Sat May 15, 2010 3:33 pm 
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Course Students


Posts: 1
What if Y is 0.
We can infer 0 or 1 from the statement 2. I think that's why the answer for this question is E.
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nwalker001
 Post subject: Re: If x=0.5, is y = 1? GMATPrep Quant DS
 Post Posted: Sat May 15, 2010 3:41 pm 
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Posts: 2
Here's how I'd solve:

If x = 0.5, is y =1?

1) (y^2)*(x+0.5) = 1
2) y*(2x-1) = 2x-1

Evaluate statement 1:
Plug 0.5 in for x
(y^2)*(0.5+0.5) = 1
(y^2)*(1) = 1
(y^2) = 1
y = 1, -1, or (1^(1/2))
Insufficient

Evaluate statement 2:
plug in 0.5 for x
y*(2(0.5)-1) = 2(0.5)-1
y*(1-1) = 1-1
y*0 = 0
y = any number
Insufficient

Evaluate statements 1 and 2 together:
y = 1, -1, or (1^(1/2)) satisfies all criteria
Insufficient

Answer E
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tim
 Post subject: Re: If x=0.5, is y = 1? GMATPrep Quant DS
 Post Posted: Mon May 24, 2010 1:10 pm 
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ManhattanGMAT Staff


Posts: 1779
Location: Southwest Airlines, seat 21C
nwalker has the right idea here. In statement 2, y can be literally any number. Obviously this won't answer the question, and since it adds no restrictions whatsoever to y, it does not help at all when combined with a statement 1 that already is insufficient..

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Tim Sanders
Manhattan GMAT Instructor
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