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# 1/p > r/(r^2+2) ? 1) p=r 2)r>0

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Manager
Joined: 19 Aug 2007
Posts: 202
1/p > r/(r^2+2) ? 1) p=r 2)r>0 [#permalink]

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15 Jun 2008, 19:26
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1/p > r/(r^2+2) ?

1) p=r
2)r>0
Director
Joined: 14 Aug 2007
Posts: 727

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15 Jun 2008, 19:55
gmat blows wrote:
1/p > r/(r^2+2) ?

1) p=r
2)r>0

Looks like C

r^2+ 2 is going to be positive

r^2 + 2/p > r

1) r^2+ 2 /r > r ; we dont know if r is + ve or -ve insuff
2) alone insuff

together,

r^2+2 > r^2 which should be true for any r>0
Intern
Joined: 06 Aug 2007
Posts: 38

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16 Jun 2008, 14:34
I get A!

With A, the eqn boils down to... r^2 + 2 > r^2

And, the above eqn holds true for all values of r (positive and negative)

Whats the OA???
Senior Manager
Joined: 12 Apr 2008
Posts: 499
Location: Eastern Europe
Schools: Oxford

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16 Jun 2008, 15:15
I agree with alpha_plus_gamma – it’s C.

Quote:
With A, the eqn boils down to... r^2 + 2 > r^2
And, the above eqn holds true for all values of r (positive and negative)

While it seems at first that a) is sufficient, it is not so. We need second condition in order to transform the inequality to the form r^2+2 > r^2. without the condition r>0, the transformation would be invalid (since it implies the multiplication of the inequality by (possibly) negative number).
Intern
Joined: 22 Apr 2008
Posts: 13

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16 Jun 2008, 16:43
I agree with C as the answer. If simple plug in chug will prove our answer

R=3

p=r

1/3 > 3/(9+2)

If the answer is only A then it can be disproven by

R=-3

1/-3 > -3/(9+2)

This results in -0.333... > -0.2727... which is False
Senior Manager
Joined: 29 Aug 2005
Posts: 272

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17 Jun 2008, 00:42
gmat blows wrote:
1/p > r/(r^2+2) ?

1) p=r
2)r>0

statement 1 is insufficent

here is how

let p = r = 2

1/2 > 2/6
this implies 1/2 > 1/3

let p = r = -1
-1/1 > -1/1

-1>-1

therefore clearly which is insufficent

statement 2 does not define p therefore it is insufficent

Both statements put together we get C which is the answer
_________________

The world is continuous, but the mind is discrete

Manager
Joined: 19 Aug 2007
Posts: 202

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17 Jun 2008, 12:00
OA is C.

used the same logic as alpha and greenoak.

thanks.

greenoak wrote:
I agree with alpha_plus_gamma – it’s C.

Quote:
With A, the eqn boils down to... r^2 + 2 > r^2
And, the above eqn holds true for all values of r (positive and negative)

While it seems at first that a) is sufficient, it is not so. We need second condition in order to transform the inequality to the form r^2+2 > r^2. without the condition r>0, the transformation would be invalid (since it implies the multiplication of the inequality by (possibly) negative number).
Re: Inequality - DS   [#permalink] 17 Jun 2008, 12:00
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