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If (x/y)^(1/2)=n, what is the value of x?

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If (x/y)^(1/2)=n, what is the value of x? [#permalink]  06 Apr 2012, 18:49
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If (x/y)^(1/2)=n, what is the value of x?

(1) (n^2)y = 100
(2) n= 5 and y = 4

[Reveal] Spoiler:
This question is from Total GMAT Math. The statement (1) provides that (n^2)y = 100 which implies that n(y^(1/2)) can be either 10 or -10. However, the solution provided by the book states that the above value is only 10. Hence I chose B, sine the statement (1) can be both 10 or -10. Is my approach incorrect?

[Reveal] Spoiler: OA
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Re: If (x/y)^(1/2)=n, what is the value of x? [#permalink]  06 Apr 2012, 21:09
Rearranging/squaring the equation given in the question saves you from the troubles with square roots.

\sqrt{\frac{x}{y}}=n
\frac{x}{y}=n^2
x=(n^2)y

Statement 1: (n^2)y=100
Hence statement 1 is sufficient.

Also if you were to continue from the equation you've arrived at,
When its 10:
n\sqrt{y}=10
(n^2)y=10^2
(n^2)y=100=x

When its -10:
n\sqrt{y}=-10
(n^2)y=(-10)^2
(n^2)y=100=x

Both lead to x=100 so statement 1 is still sufficient.
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Re: If (x/y)^(1/2)=n, what is the value of x? [#permalink]  07 Apr 2012, 02:06
andrewh wrote:
1) (n^2)y = 100
2) n= 5 and y = 4

This question is from Total GMAT Math. The statement (1) provides that (n^2)y = 100 which implies that n(y^(1/2)) can be either 10 or -10. However, the solution provided by the book states that the above value is only 10. Hence I chose B, sine the statement (1) can be both 10 or -10. Is my approach incorrect?

Given that
(x/y)power(1/2) = n
x/y = n square
x = y. n square

now,

1. y.nsquare = 100
sufficient

2. values for Y and N are given, then this is sufficient too...

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Re: If (x/y)^(1/2)=n, what is the value of x? [#permalink]  07 Apr 2012, 09:01
Thanks so much. I can believe I didn't see that .
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Re: If (x/y)^(1/2)=n, what is the value of x? [#permalink]  23 May 2013, 06:37
reddevil00 wrote:
If (x/y)^(1/2)=n, what is the value of x?

(1) (n^2)y = 100
(2) n= 5 and y = 4

This question is from Total GMAT Math. The statement (1) provides that (n^2)y = 100 which implies that n(y^(1/2)) can be either 10 or -10. However, the solution provided by the book states that the above value is only 10. Hence I chose B, sine the statement (1) can be both 10 or -10. Is my approach incorrect?

yes, what u have misses is : l x l is +/- and again the same way x^2 is always positive but a root need not be, here we have square only dude.
Re: If (x/y)^(1/2)=n, what is the value of x?   [#permalink] 23 May 2013, 06:37
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