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(I) a=2b
S=1/2b^2*(3b-1) depending on b's value. insufficient
(II) a+b>1
a+b-1>0
depending on the signs of a and b
Combine
2b^2>0
a+b-1>0
S>0
Sufficient

"C".....altho I am assuming from the eqn that a and b <> 0...as it will make 1/b or 1/a...infinity,
now....we have ab/a+b and ab as 2 eqn

I....if a = 2b....then.....first one becomes 2b/3 and second is 2b^2.....if b < 0....then 2nd one is > ....if b
is >=1....then 2nd is >....if 0<b<1....say b = 1/4.....then first is >....so insuff

II...if a+b > 1.....first ab/a+b is always < than ab, if ab is +ve and > ab is ab is -ve...so insuff...

Combine
a = 2b and a+b > 1
b > 1/3....so b +ve......and a is +ve.....so from II.....we get ab/a+b < ab...suff

Last edited by banerjeea_98 on 03 Feb 2005, 10:27, edited 1 time in total.