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Is the positive integer N a perfect square?

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jnelson0612
 Post subject: Re: Is the positive integer N a perfect square?
 Post Posted: Sun Nov 20, 2011 12:47 am 
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ManhattanGMAT Staff


Posts: 1857
The answer to this problem is D. Let us know if you need more clarification.

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Jamie Nelson
ManhattanGMAT Instructor
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shetty.nagraj1
 Post subject: Re: Is the positive integer N a perfect square?
 Post Posted: Sun Jan 29, 2012 4:07 pm 
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Students


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jnelson0612 wrote:
The answer to this problem is D. Let us know if you need more clarification.


Hi,

The explanation says " the sums of the factors are odd" -- which is makes sense and is correct.

however in the stem, the second statement states "(2) The sum of all distinct factors of N is even."

Then the answer should be A, shouldnt it?

Pls can you help me understand if I am missing something here.

Thank you.
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tim
 Post subject: Re: Is the positive integer N a perfect square?
 Post Posted: Thu Feb 02, 2012 7:58 pm 
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Posts: 2242
Location: Southwest Airlines, seat 21C
if a number is to be a square, its factors have to add to an odd number. this is true. now with that in mind let's take a look at statement 2 and ask if it helps to answer the question:

the question is: is N a perfect square?

statement 2 says the factors of N add to an even number. from this we conclude that N must not be a perfect square. now let's answer the question:

is N a perfect square? NO!

we know the answer to the question - it is NO!

remember, whenever you KNOW the answer to the question - as we do here - the statement is sufficient. so statement 2 is sufficient.

the ONLY time a statement is insufficient is when it does not answer the question at the top of the page.

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Tim Sanders
Manhattan GMAT Instructor
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shetty.nagraj1
 Post subject: Re: Is the positive integer N a perfect square?
 Post Posted: Thu Feb 02, 2012 8:16 pm 
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thank you Tim.

I realized that I overlooked the sufficiency in getting No from both the statements. my bad.

I ll take care next time.

thanks again.

cheers.
Nagraj
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jnelson0612
 Post subject: Re: Is the positive integer N a perfect square?
 Post Posted: Sun Feb 05, 2012 5:32 pm 
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Posts: 1857
Great!

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Jamie Nelson
ManhattanGMAT Instructor
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