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Please tell the flaw in my logic. Q 145 OG 11 ...Plz help

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by swati.sug » Mon Jul 14, 2008 2:40 pm
Is 1/p >r/(r^2 +2)
1. p = r
2.r > 0


Plz help..
Let me know what am I doing wrong if I solve it as below:

Cross multiplying the ques stem:

r^2 + 2 > pr

Is r^2 -pr +2 >0 ...This is what is asked..
Considering statement 1. p = r

Substituting in r^2 -pr + 2 > 0,
First two terms will cancel out regardless of whether both p and q are posiive or negative.

and remaining 2 > 0 is definatilely true.

So I selected OA) AStatement 1 is sufficent.

Please tell flaw in my logic.
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Source: — Data Sufficiency |

swati.sug wrote:Is 1/p >r/(r^2 +2)
1. p = r
2.r > 0


Plz help..
Let me know what am I doing wrong if I solve it as below:

Cross multiplying the ques stem:

r^2 + 2 > pr


Is r^2 -pr +2 >0 ...This is what is asked..
Considering statement 1. p = r

Substituting in r^2 -pr + 2 > 0,
First two terms will cancel out regardless of whether both p and q are posiive or negative.

and remaining 2 > 0 is definatilely true.

So I selected OA) AStatement 1 is sufficent.

Please tell flaw in my logic.
I've highlighted above the mistake. You can't cross multiply here unless you know whether p is positive or negative; if p is negative, you would need to reverse the inequality.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
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by swati.sug » Tue Jul 15, 2008 7:46 am
Thanks Ian

So what is the rights method to solve it.

Is it reversing the sign of the inequality when I consider the negative value(after cross mutiplying and simplifying).

Please illustrate ..
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by sm612 » Tue Jul 15, 2008 8:24 am
Apart from +ve, -ve values, (1) does not tell if r=0.
If this is the case then, we cannot find the result.

Combining 1 and 2 we can tell the answer. So C should be the answer.

What is OA?
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