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gmat prep - even integers

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by airmiles5 » Tue Apr 07, 2009 4:43 pm
Having some trouble with the following data sufficiency question:


If x and y are positive integers, is x an even integer?

(1) x (y+5) is an even integer.
(2) 6y^2 + 41y + 25 is an even integer.


Was able to rule out A,B,D very quickly but incorrectly chose C.

It seems that to satisfy (2) y must be odd. Plugging an odd value for y into (1), means that x must be even?

Obviously my thinking is flawed somehow, can anyone explain why the answer is E?
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Source: — Data Sufficiency |

Re: gmat prep - even integers

by Ian Stewart » Tue Apr 07, 2009 7:03 pm
airmiles5 wrote:Having some trouble with the following data sufficiency question:


If x and y are positive integers, is x an even integer?

(1) x (y+5) is an even integer.
(2) 6y^2 + 41y + 25 is an even integer.


Was able to rule out A,B,D very quickly but incorrectly chose C.

It seems that to satisfy (2) y must be odd. Plugging an odd value for y into (1), means that x must be even?

Obviously my thinking is flawed somehow, can anyone explain why the answer is E?
You've analyzed statement 2 correctly, so I won't go through it; Statement 2 just tells you that y must be odd. Now, if y is odd, then y+5 will be even. So x(y+5) will be even no matter what the integer x is, and we don't have enough information to decide whether x is odd or even.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
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by airmiles5 » Tue Apr 07, 2009 7:30 pm
Thanks. I get it. I have no idea why I thought x needed to be even there.

Here's hoping I'm getting all these brain cramps out of my system before tomorrow.
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