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DS 2

by magical cook » Wed Nov 28, 2007 11:13 am
If a and b are positive, is (a^-1 + b^-1)^-1 less than (a^-1b^-1)^-1?
(1) a = 2b
(2) a + b > 1




Hi, [spoiler]I am getting cnfused since a b could be non-integer... can anyone help? [/spoiler]
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by Suyog » Wed Nov 28, 2007 11:31 am
The first term - (a^-1 + b^-1)^-1

for any positive value of a and b the first term will always be positive.
coz a^-1 & b^-1 will always be negative so as their addition and then ^-1 of that number will always result in the positive value.

The second term - (a^-1b^-1)^-1
for any positive value of a and b the first term will always be negative.
coz a^-1 & b^-1 will always be negative and their multiplication will always be positive, now ^-1 of the positive number will be again a negative.

So Ans shud be D.
let me know.
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by magical cook » Wed Nov 28, 2007 12:02 pm
Sorry, it's wrong.. :( can anyone help us??
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by ri2007 » Wed Nov 28, 2007 2:08 pm
The ans should be C

The lowest values for which a = 2b and a + b > 0 are

b = 0.4 and a = 0.8.

if u put these values or any values greter than then in all cases u will find ab/a+b is less than ab

pls confirm
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by magical cook » Wed Nov 28, 2007 2:36 pm
Sorry, it's wrong too.. hmm
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by lawalx » Wed Nov 28, 2007 3:29 pm
the answer dhould be A. pls confirm
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by maverick2007 » Wed Nov 28, 2007 4:53 pm
The ans is A


When we simplify the inequality it comes out to be

Is ab/(a+b)<a/b?

now statement 1 is sufficient to answer this question...

OA please
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by syv11 » Wed Nov 28, 2007 8:33 pm
Hey, I get to ab/(a+b)<ab when simplifying it. Then 1<a+b

Therefore A not sufficient.
B is.
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by samirpandeyit62 » Thu Nov 29, 2007 12:03 am
Agree with syv11 it should be B
Regards
Samir
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by gabriel » Thu Nov 29, 2007 2:28 am
B for me too ..
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by sankruth » Thu Nov 29, 2007 3:01 am
B for me...

Can Magical cook reveal the answer...cos the suspense is killing me!! :x
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by magical cook » Thu Nov 29, 2007 4:16 am
Oops soory for the late reply..... Yes B is the answer. thank you!
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