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Data Sufficiency - Manipulations

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Data Sufficiency - Manipulations

by phoenix9801 » Sat Jan 01, 2011 5:23 pm
Is XY = -1 ?

(1) x = y
(2) y = 1

My question is how come statement (1) is sufficient?
The Gmat said if x = y, then the question can be rephrased thus: x^2= -1? (I do not see the connect how do you move from x=y to x^2= -1 ???)

Also if you want to combine both statements it would be x =y=1. How is it the same as xy =1 (come someone please explain)


I would greatly appreciate it if you can explain in details...
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by anshumishra » Sat Jan 01, 2011 5:50 pm
phoenix9801 wrote:Is XY = -1 ?

(1) x = y
(2) y = 1

My question is how come statement (1) is sufficient?
The Gmat said if x = y, then the question can be rephrased thus: x^2= -1? (I do not see the connect how do you move from x=y to x^2= -1 ???)

Also if you want to combine both statements it would be x =y=1. How is it the same as xy =1 (come someone please explain)


I would greatly appreciate it if you can explain in details...
xy = -1 ?

Statement 1:
x = y
=> xy = x^2 This will never be -1 -> as x,y belongs to the set of real number
Sufficient -> As we can say xy!= -1 or xy is never equal to -1.

Statement 2 :
y=1
=> xy = x; Not Sufficient (As if x=-1, then xy = -1 else xy is not equal to -1)

Hence A.
Thanks
Anshu

(Every mistake is a lesson learned )
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