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OG 11th, DS #119

Expert replies
Source: — Data Sufficiency |

by scoobydooby » Thu Mar 05, 2009 4:58 am
Is 2x-3y<x^2 ?

1. 2x-3y<-2
=> 2x-3y<0
x^2>0

=>2x-y<x^2 sufficiennt


2. x>2, y>0
for x>2, 2x<x^2
=>2x-3y<x^2 (we are subtracting a positive number from something that is already less than x^2, therby making it still lesser
sufficent

hence D
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by bluementor » Thu Mar 05, 2009 5:07 am
Statement 1:
A square of any number will always be non-negative. So, x^2 must be a non-negative number. If we already know that 2x-3y is less than -2, then we are sure that 2x-3y is less than x^2. Sufficient.

Statement 2:

Is 2x - 3y < x^2 ?
Is x^2 - 2x > -3y ?
Is x(x-2) > -3y ?

Since y>0, -3y can only be a negative number.
Since x>2, x(x-2) can only be positive.

Therefore, we can prove that x(x-2) is always larger than -3y. Sufficient.

Choose D.

-BM-
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by vkb16 » Sat Mar 07, 2009 1:01 am
fantastic replies both of you!

thanks a lot!
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