sum of the squares

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DavoodBeater: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Mon Nov 17, 2008 7:04 am; Thanked: 1 times

by DavoodBeater » Tue Jan 13, 2009 1:18 pm

What is the question looking for? which logic?
since both [8, 3, and 2] and [7, 5, and 1] can give 13 here. But i dont understand what the question is looking for.
Thanks.
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Source: Beat The GMAT — Problem Solving | Tue Jan 13, 2009 1:18 pm

Mr2Bits: Senior | Next Rank: 100 Posts; Posts: 73; Joined: Wed Jan 07, 2009 1:00 pm; Location: Tampa, FL; Thanked: 9 times; GMAT Score:630

by Mr2Bits » Tue Jan 13, 2009 1:44 pm

[8, 3, and 2] does not add up to 75 be careful with quick addition

64 + 9 + 4 = 77

Your answer is 7, 5, and 1

49 + 25 + 1 = 75

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DavoodBeater: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Mon Nov 17, 2008 7:04 am; Thanked: 1 times

by DavoodBeater » Tue Jan 13, 2009 2:10 pm

yes, you are right.
But I am still confused, since i dont understand the point of the question. the only way to answer this question that I know is plugging numbers. is there any other rational solution?

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Mr2Bits: Senior | Next Rank: 100 Posts; Posts: 73; Joined: Wed Jan 07, 2009 1:00 pm; Location: Tampa, FL; Thanked: 9 times; GMAT Score:630

by Mr2Bits » Tue Jan 13, 2009 4:11 pm

Only way I know is to lay out the sums of the squares from 1-10 and find the combination

1 4 9 14 25 36 49 64 81 100

You can throw out 9 and 10 immediately. After that it's process of elimination.

Im sure there is some way to break 75 down into smaller roots or some other numbers trick. Im too new to my studies to know any of these yet but Im sure one of the elders will chime in.

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logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

Re: sum of the squares

by logitech » Tue Jan 13, 2009 5:02 pm

DavoodBeater wrote:What is the question looking for? which logic?
since both [8, 3, and 2] and [7, 5, and 1] can give 13 here. But i dont understand what the question is looking for.
Thanks.
Question from GMATPrep

(x+y+z)^2 = x^2+y^2+z^2 +2(xy+yz+zx)

= 75+2(blablabla)

And this sum will be a perfect square.

81
100
121
144
169
196
etc...

if you look the difference between this numbers and 75

6
25
46
69
94
121
etc..

You will see that only 6, 46 and 94 can be the options since they can ve divided into two...

YOU CAN KEEP going like this if you really love math and spend some time

or you can apply plugging numbers

LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

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