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Source: — Data Sufficiency |

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by Rahul@gurome » Mon Aug 30, 2010 6:25 am
pradeepkaushal9518 wrote:is x^2 equal to xy?

1.x^2-y^2=(x+5)(y-5)

2.x=y
(1) x^2 - y^2 = xy + 5y - 5x - 25
x^2 + 5x + 25 = y^2 + 5y + xy
But this does not give any info on whether x^2 equal to xy.
So, (1) is NOT SUFFICIENT.

(2) x= y implies x^2 = xy
So, (2) is SUFFICIENT.

The correct answer is [spoiler](B)[/spoiler].
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by Gurpinder » Mon Aug 30, 2010 9:37 am
Hey Rahul,

Can you tell me what I am doing wrong?

The way I thought of it, statement 1 is sufficient.

(1) x^2-y^2=(x+5)(y-5)

Can't we use this to get the values for X and Y?

X= -5 and Y = 5

Therefore x^2=25 and (5)(-5)=-25

So Stmt 1 is sufficient?

Please advise,
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by puneetdua » Mon Aug 30, 2010 10:17 am
Hi,

In my first attemp i also thought answer is B but after reading Guprinder's comments - i lost the confidence in option B ...

i tried putting several values in option 1 to satisfy the relation but only -5 / 5 are satisgying - so D might be the answer ...

curious to know the OA..Pradeep can you please post the answer please..
Thanks
Puneet
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by reply2spg » Mon Aug 30, 2010 11:54 am
Answer should be B. Here's how I got it,

A. x^2-y^2=(x+5)(y-5)

which means
x^2-y^2 = x^2 - 25

get rid of x^2 from both sides. you will get

y^2 = 25 and y = 5 or -5. You don't know x. so you can not say x^2=xy.
Gurpinder wrote:Hey Rahul,

Can you tell me what I am doing wrong?

The way I thought of it, statement 1 is sufficient.

(1) x^2-y^2=(x+5)(y-5)

Can't we use this to get the values for X and Y?

X= -5 and Y = 5

Therefore x^2=25 and (5)(-5)=-25

So Stmt 1 is sufficient?

Please advise,
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by Stuart@KaplanGMAT » Mon Aug 30, 2010 1:04 pm
Gurpinder wrote:Hey Rahul,

Can you tell me what I am doing wrong?

The way I thought of it, statement 1 is sufficient.

(1) x^2-y^2=(x+5)(y-5)

Can't we use this to get the values for X and Y?

X= -5 and Y = 5

Therefore x^2=25 and (5)(-5)=-25

So Stmt 1 is sufficient?

Please advise,
Hi,

x=5 and y=5 also makes the statement correct:

25 - 25 = (10)(0)

So, based on (1), the values could be:

x=-5 y=5; does (-5)^2 = (-5)(5)? NO

x=5 y=5; does (5)^2 = (5)(5)? YES
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