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Senior | Next Rank: 100 Posts
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by yangliu0401 » Tue Mar 10, 2009 2:43 pm
Is 1/P > R/(R²+2)?

1). P=R
2). R>0

OA is C.

While I choose A.

first, we can dedrive from the inequality above :

1/P > R/(R²+2)=>R²+2>R*P

accoding to 1), the new inequality could be R²+2>R², sufficient
2). not sufficient.

Any comment? :oops:
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by cramya » Tue Mar 10, 2009 2:58 pm
1/P > R/(R²+2)=>R²+2>R*P

The corss multiplication is not allowed since we dont know p,r are negative or positive. If its positive then what u did is ok but we dont know from stm I since all we know is p=r.If its negative the inequality reverses.

This is a trap which we can fall in to when manipulating inequalities.

Q:

Is 1/p > r/r^2+2

Stmt I

p=r

Is 1/r > r/r^2+2

(or) Is 1/r-r/r^2+2 >0

(or) Is r^2+2-r^2/r(r^2+2) > 0

(or) Is 2/ r(r^2+2) > 0

We have no idea if r is positive or negative so INSUFF

Stmt II

r > 0

No idea about p.

INSUFF

Together:


since r>0, 2/ r(r^2+2) > 0 always greater than 0

Choose C

Hope this helps ;let me know if u still hv questions.

Regards,
CR
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by yangliu0401 » Tue Mar 10, 2009 3:11 pm
cramya wrote:
1/P > R/(R²+2)=>R²+2>R*P

The corss multiplication is not allowed since we dont know p,r are negative or positive. If its positive then what u did is ok but we dont know from stm I since all we know is p=r.If its negative the inequality reverses.

This is a trap which we can fall in to when manipulating inequalities.

Q:

Is 1/p > r/r^2+2

Stmt I

p=r

Is 1/r > r/r^2+2

(or) Is 1/r-r/r^2+2 >0

(or) Is r^2+2-r^2/r(r^2+2) > 0

(or) Is 2/ r(r^2+2) > 0

We have no idea if r is positive or negative so INSUFF

Stmt II

r > 0

No idea about p.

INSUFF

Together:


since r>0, 2/ r(r^2+2) > 0 always greater than 0

Choose C

Hope this helps ;let me know if u still hv questions.

Regards,
CR

woow~~~
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by moorthy76 » Wed Mar 11, 2009 1:44 am
cool... thanks
Best Regards,
Surya
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