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If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4

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If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4 [#permalink]

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New post 10 Oct 2017, 01:07
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Question Stats:

39% (00:59) correct 61% (00:55) wrong based on 34 sessions

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GMAT 1: 620 Q46 V29
Re: If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4 [#permalink]

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New post 10 Oct 2017, 02:45
(a) so we replace 2z for y. therefore x2z = z. we divide 2z in each side, and x = 1/2 = sufficiente

(b) we take the square root in both sides, so y = +-2. when we replace the values into the equation we can see that we get two different solutions, either +1 or -1. therefore insufficient.

I would say A
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Re: If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4 [#permalink]

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New post 10 Oct 2017, 04:18
(A) 2xz=z, if z is not zero we can cancel it and x =1/2 ,but if z=0 then we can't cancel it on both side and x can have any value. So option A is insufficient.
(B) y=+2 or -2 , still we don't know value of z. So we can't find value of x.


But if we take both options at a time we put y=2 in option A we get z=1 and x=1/2 , if we put y=-2 in option A we get z=-1 and x=1/2.
So both options are necessary to ans the qs.


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If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4 [#permalink]

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New post 14 Oct 2017, 18:13
Bunuel wrote:
If xy = z, what is the value of x ?

(1) y =2z
(2) y^2 = 4


(1) => 2zx = z => z(2x-1) = 0 => z=0 or x=1/2
If z=0 then y=0, x can take any value.
So insufficient.

(2) => y= +/- 2
Insufficient to find x.

(1) + (2) => With y=2, then z=1, x=1/2
With y=-2, then z=-1, x=1/2
Same x value in both cases.
So C is the answer.
If xy = z, what is the value of x ? (1) y =2z (2) y^2 = 4   [#permalink] 14 Oct 2017, 18:13
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