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

[zarak_khan]

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!

[mkim1213]

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.

[nwalker001]

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

[tim]

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..