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Source: — Data Sufficiency |

by schumi_gmat » Sun Mar 07, 2010 12:36 pm
1) x^4 - x^3 > 0
i.e. x^3 (x-1) >0

The above will be true if bot x^3 >0 and x-1>0 or x^3 < 0 and x-1 <0
Two answers ....Insuff

2) x^5 - x^3 > 0
x^3 (x-1) (x+1) >0
using same concept above, Again multiple answers and hence insuff.

Combining, we cannot get unique answer


Hence E
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by raisethebar » Mon Mar 08, 2010 12:52 am
schumi_gmat wrote:1) x^4 - x^3 > 0
i.e. x^3 (x-1) >0

The above will be true if bot x^3 >0 and x-1>0 or x^3 < 0 and x-1 <0
Two answers ....Insuff

2) x^5 - x^3 > 0
x^3 (x-1) (x+1) >0
using same concept above, Again multiple answers and hence insuff.

Combining, we cannot get unique answer


Hence E
Can we really work like this with inequalities?

X<1 then can we say X-1<0?
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by schumi_gmat » Mon Mar 08, 2010 10:15 pm
There is nothing wrong in subtracting values on both sides

Be careful when you cross multiply or Divide.
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by neoreaves » Sun Mar 28, 2010 6:52 am
IMO B

2) x^3 < x^5

This is only true for x>1 ....we can test other values

x = fraction ....this won't be true for fractions so discard

x = negative integers ....wont be true either so the only way this can be true is x > 1


I disagree with the OA = E ....unless someone can give a counter example to prove this is not sufficient.
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by gmatmachoman » Sun Mar 28, 2010 10:13 am
neoreaves wrote:IMO B

2) x^3 < x^5

This is only true for x>1 ....we can test other values

x = fraction ....this won't be true for fractions so discard

x = negative integers ....wont be true either so the only way this can be true is x > 1


I disagree with the OA = E ....unless someone can give a counter example to prove this is not sufficient.
Bro..

But again going by ur wrds that X >1, then u shuld have opted D. Still it is WRONG!!

here is the catch!

Did u try for X =0.5,0.25 etc??

Logic shall fail!!
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by neoreaves » Sun Mar 28, 2010 11:52 am
gmatmachoman wrote:
neoreaves wrote:IMO B

2) x^3 < x^5

This is only true for x>1 ....we can test other values

x = fraction ....this won't be true for fractions so discard

x = negative integers ....wont be true either so the only way this can be true is x > 1


I disagree with the OA = E ....unless someone can give a counter example to prove this is not sufficient.
Bro..

But again going by ur wrds that X >1, then u shuld have opted D. Still it is WRONG!!

here is the catch!

Did u try for X =0.5,0.25 etc??

Logic shall fail!!
ok i see your point ...though your example of x = 0.5 or 0.25 wont work ....

but x = -0.5 will ...so yeah it should be E
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by gmatmachoman » Sun Mar 28, 2010 10:35 pm
neoreaves wrote:
gmatmachoman wrote:
neoreaves wrote:IMO B

2) x^3 < x^5

This is only true for x>1 ....we can test other values

x = fraction ....this won't be true for fractions so discard

x = negative integers ....wont be true either so the only way this can be true is x > 1


I disagree with the OA = E ....unless someone can give a counter example to prove this is not sufficient.
Bro..

But again going by ur wrds that X >1, then u shuld have opted D. Still it is WRONG!!

here is the catch!

Did u try for X =0.5,0.25 etc??

Logic shall fail!!
ok i see your point ...though your example of x = 0.5 or 0.25 wont work ....

but x = -0.5 will ...so yeah it should be E
hahahhaa..nice catch...Yeah it should have been x=-0.5,-0.25...Seems sunday midnite blues has struck me!
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