Square root

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fleurdelisse: Senior | Next Rank: 100 Posts; Posts: 44; Joined: Tue Feb 03, 2009 2:01 am; Thanked: 1 times

by fleurdelisse » Fri Apr 17, 2009 11:07 am

If x and y are both positive, which of the following myst be greater than 1/(sqrt(x+y))

I. sqrt(x+y)/2x
II. sqrtx+sqrty/(x+y)
III. sqrtx - sqrty/(x+y)

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Source: Beat The GMAT — Problem Solving | Fri Apr 17, 2009 11:07 am

DanaJ: Site Admin; Posts: 2567; Joined: Thu Jan 01, 2009 10:05 amFollowed by: 550 members; Thanked: 712 times; GMAT Score:770

by DanaJ » Fri Apr 17, 2009 1:36 pm

I have my doubts about this problem. Could you please double-check to see of it's written correctly? Of course, I might be missing smth...

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dumb.doofus: Master | Next Rank: 500 Posts; Posts: 435; Joined: Sat Sep 27, 2008 2:02 pmFollowed by: 1 member; Location: San Jose, CA; Thanked: 43 times; GMAT Score:720

by dumb.doofus » Fri Apr 17, 2009 9:25 pm

IMO B

If I break it down, what we have to compare is:
a) x+y > 2x
b) root(x+y)*(root(x)+root(y)) > x+y
c) root(x+y)*(root(x)-root(y)) > x+y

If you choose values for x and y, 1,1 and 1,2 and 2,1, you'll see that only b stands out.

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