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Advanced GMAT Quant Try It Question 3-2

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jeffr555
 Post subject: Advanced GMAT Quant Try It Question 3-2
 Post Posted: Sun Aug 07, 2011 10:21 pm 
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Course Students


Posts: 3
Hi,

Statement: Is the integer n odd?

(1) n squared - 2n is not a multiple of 4.

the answer says this is sufficient to say that n has to be odd. I dont understand why n can't be 2 or 0, making the statement insufficient. Could you explain the reasoning please.

Thanks for your help.
Jeff
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mithunsam
 Post subject: Re: Advanced GMAT Quant Try It Question 3-2
 Post Posted: Mon Aug 08, 2011 10:03 am 
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Course Students


Posts: 76
Statement 1 -> n^2-2n is not a multiple of 4

If n is even (E), then the equation will become E^2 -2E
=E*E - 2*E
But, 2 is a prime factor for every even. So, we can write E = 2*x, where x is any number

So the equation becomes (2*x)*(2*x) - 2*(2*x) = 4x^2-4x=4(x^2-x). This is a multiple of 4.

Therefore, if n is even, then n^2-2n will be a multiple of 4. But statement states that n^2-2n is not a multiple of 4. Hence, n is not even (otherwise, n is odd).


Note to Jeff (n=2 or n=0 will make n^2-2n = 0. However, 0 is a multiple of every number. So n cannot be either of these two values)


Last edited by mithunsam on Thu Aug 18, 2011 1:14 pm, edited 1 time in total.

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jnelson0612
 Post subject: Re: Advanced GMAT Quant Try It Question 3-2
 Post Posted: Wed Aug 17, 2011 6:01 pm 
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ManhattanGMAT Staff


Posts: 1857
Very, very nice!

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Jamie Nelson
ManhattanGMAT Instructor
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