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GMATPrep equation problem


 
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netigen
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PostPosted: Mon May 12, 2008 2:15 am    Post subject: GMATPrep equation problem Reply with quote
Help me get this one right.

I thought we can solve for XY using both the equations if we subtract one equation from another we get

x^2 = x or x=1 and hence, y=2

OA is E
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amitansu
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PostPosted: Mon May 12, 2008 2:19 am    Post subject: Reply with quote
Netigen, you are right.
Ans should be C.


Amit
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akshatsingh
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PostPosted: Mon May 12, 2008 10:03 pm    Post subject: Reply with quote
x^2 = x doesnt mean x = 1.

it means x(x-1) = 0
=> x=0 or x=1

Clearly a unique xy cannot be found out using these values of x.


I believe answer should be E.
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netigen
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PostPosted: Mon May 12, 2008 10:39 pm    Post subject: Reply with quote
I knew I was doing something stupid Cool, thanks for pointing it out.
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gabriel
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PostPosted: Tue May 13, 2008 12:28 pm    Post subject: Reply with quote
akshatsingh wrote:
x^2 = x doesnt mean x = 1.

it means x(x-1) = 0
=> x=0 or x=1

Clearly a unique xy cannot be found out using these values of x.


I believe answer should be E.


This is a very common mistake committed in DS. We have to remember any quadratic equation will have 2 roots. So never ever stop after you find one value for x if there is a term x^2 in the equation.

Regards
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