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If x and y are +ve, which must greater than 1/(x+y)^0.5?

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pankaj_kamat
 Post subject: If x and y are +ve, which must greater than 1/(x+y)^0.5?
 Post Posted: Thu Dec 10, 2009 7:05 am 
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Students


Posts: 2
(i) ((x+y)^0.5) / 2x

(ii) (x^0.5 + y^0.5) / (x+y)

(iii) (x^0.5 - y^0.5) / (x+y)

A. None
B. I only
C. II only
D. I and III
E. II and III

Source: GMATPrep

OA C (I chose A)

Its not clear to me how (II) could be right. I tried with values of x = 1/9 and y = 1/16 and 1/(x+y) ^ 0.5 = 5 (II) comes to (1/3 + 1/4) / (1/9 + 1/16) which comes to roughly 3.5

The question does not say these are integers. I am assuming GMATPrep is usually right about answers, so surely I am missing something here. Please help!
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jerly_vivek
 Post subject: Re: If x and y are +ve, which must greater than 1/(x+y)^0.5?
 Post Posted: Sun Dec 13, 2009 4:09 am 
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Students


Posts: 19
for x=1/9 and y = 1/16:
question stem gives: Sqrt[1/(25/144)]
=sqrt[144/25]=12/5=2.40

while ii gives 3.XX for x and y.

It is simple calculation. can you please tell your excat doubt.
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pankaj_kamat
 Post subject: Re: If x and y are +ve, which must greater than 1/(x+y)^0.5?
 Post Posted: Wed Dec 16, 2009 5:54 am 
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Students


Posts: 2
I made that simple calculation mistake. Thanks for pointing it out! :)
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RonPurewal
 Post subject: Re: If x and y are +ve, which must greater than 1/(x+y)^0.5?
 Post Posted: Sat Jan 09, 2010 4:56 am 
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ManhattanGMAT Staff


Posts: 7146
this is one of the most often posted questions on this forum; please take the time to do a search.

here are three of the threads:

if-x-and-y-are-positive-t3089.html

if-x-and-y-are-positive-which-of-the-following-t4086.html

post4838.html

--

also, please take the extra second or two to type out the words "positive" and "negative". thank you.
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