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Root Question

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jasonmaehara
 Post subject: Root Question
 Post Posted: Mon Apr 11, 2011 6:11 pm 
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Students


Posts: 23
Couldn't find this in any search so here it goes. Overall I'd say I'm okay with root however this problem seems to be giving me some trouble...

(√(90+√80) + √(90-√80))^2

Answer: 20

I know it's in the format of x^2+2xy+y^2 but I'm having trouble expanding the middle term.


Last edited by jasonmaehara on Wed Apr 13, 2011 9:49 pm, edited 1 time in total.

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RonPurewal
 Post subject: Re: Root Question
 Post Posted: Wed Apr 13, 2011 5:18 am 
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ManhattanGMAT Staff


Posts: 7146
per our forum rules, please post the problem with all of its answer choices, and then we'll answer it. (this will help especially in this case, because, as you will see, there's a good backup method based on the answer choices.)

by the way, here's a square root sign that you can copy and paste in order to make the question more legible:
√
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jasonmaehara
 Post subject: Re: Root Question
 Post Posted: Wed Apr 13, 2011 9:32 pm 
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Students


Posts: 23
My apologies.

A) 1
B) 9 - 4√5
C) 18 - 4√5
D) 18
E) 20

OA: E
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tim
 Post subject: Re: Root Question
 Post Posted: Fri Apr 15, 2011 9:19 pm 
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ManhattanGMAT Staff


Posts: 2242
Location: Southwest Airlines, seat 21C
as Ron mentioned, there is a great shortcut method for this problem. just estimate the answer and you'll see you can eliminate some wrong answers. as for helping you further though, i'd like to see what work you did on expanding and where you got hung up. i'd also like to see you copy the question correctly, because the question you have written does not have an answer of 20..

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Tim Sanders
Manhattan GMAT Instructor
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