Math questions from any Manhattan Prep GMAT Computer Adaptive Test.
hima.batavia
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If x and y are non-zero integers

by hima.batavia Sat Nov 06, 2010 2:08 am

If x and y are non-zero integers and |x| + |y| = 32, what is xy?

(1) -4x - 12y = 0

(2) |x| - |y| = 16


I don't understand why you assume that x and y are opposite signs based on simplifying the first expression.

Thanks!
Hima
jnelson0612
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Re: If x and y are non-zero integers

by jnelson0612 Sat Nov 06, 2010 9:26 pm

Hi Hima,
Take a look at the first expression, statement 1. You have
-4x - 12y = 0.

If I add 12y to both sides, I get -4x = 12y. If I divide both sides by -4, I get x=-3y.

If x = -3y, then we have the following two scenarios. Either:
a) x is positive and y is negative
OR
b) x is negative and y is positive

Notice how it is impossible for both to be negative or positive.

I hope this helps!
Jamie Nelson
ManhattanGMAT Instructor
hima.batavia
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Re: If x and y are non-zero integers

by hima.batavia Mon Nov 29, 2010 2:19 am

Thanks Jamie!

I have a follow-up question. Why do you convert them back to absolute values? When do you use that technique as a general rule?

Cheers,
Hima
jnelson0612
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Re: If x and y are non-zero integers

by jnelson0612 Mon Nov 29, 2010 3:13 pm

hima.batavia Wrote:Thanks Jamie!

I have a follow-up question. Why do you convert them back to absolute values? When do you use that technique as a general rule?

Cheers,
Hima


Hi Hima,
Sorry, I'm not understanding your question "why do you convert them back to absolute values?" Can you elaborate?

Thank you!
Jamie Nelson
ManhattanGMAT Instructor
rite2deepti
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Re: If x and y are non-zero integers

by rite2deepti Wed Dec 01, 2010 10:40 am

jnelson0612 Wrote:
hima.batavia Wrote:Thanks Jamie!

I have a follow-up question. Why do you convert them back to absolute values? When do you use that technique as a general rule?

Cheers,
Hima


Hi Hima,
Sorry, I'm not understanding your question "why do you convert them back to absolute values?" Can you elaborate?

Thank you!

What is the OA I am getting B as my answer
jnelson0612
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Re: If x and y are non-zero integers

by jnelson0612 Fri Dec 03, 2010 2:35 am

rite2deepti, the correct answer is A.

See this link to read the full explanation: cat-question-opposite-signs-t1514.html

Thank you,
Jamie Nelson
ManhattanGMAT Instructor
PoonamS895
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Re: If x and y are non-zero integers

by PoonamS895 Tue Feb 07, 2017 6:34 pm



I'm not sure why statement 2 is not sufficient.
RonPurewal
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Re: If x and y are non-zero integers

by RonPurewal Wed Feb 08, 2017 4:57 am

PoonamS895 Wrote:I'm not sure why statement 2 is not sufficient.


all you can figure out from statement 2 (plus the prompt) is that |x| = 24 and |y| = 8.
this means that x could be either 24 or –24, and y could be either 8 or –8.
thus there are two different possible values of xy (with opposite signs).