Math questions from any Manhattan Prep GMAT Computer Adaptive Test.
cschmidlapp
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If y is not equal to 4, x is not equal to 0...

by cschmidlapp Thu Jun 27, 2013 9:26 am

This question came up in my last CAT.

"If y is not equal to 4, x is not equal to 0, and y^2-16/3x = y-4/6, then in terms of x, y equals?"

I have two questions - if y is not equal to 4, what is the math rule that allows you to eliminate the two (y-4)s when they aren't set equal to 0?

Second - in the MGMAT explanation, once simplified, you get down to y+4 = x/2, but then the next step and answer is y = x-8/2. How do you get the 8? Shouldn't it be x/2-4?
RonPurewal
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Re: If y is not equal to 4, x is not equal to 0...

by RonPurewal Fri Jun 28, 2013 5:54 am

cschmidlapp Wrote:This question came up in my last CAT.

"If y is not equal to 4, x is not equal to 0, and y^2-16/3x = y-4/6, then in terms of x, y equals?"


granted, it can be difficult to format mathematical expressions on a forum, but please try to format these statements so that they are easier to read and less ambiguous.

from context, it appears that this statement is supposed to say ...
(y^2 - 16) / 3x = (y - 4) / 6
is that what it's supposed to say? please confirm, thanks.

disclaimer: the explanations below assume that my formulation of the problem is correct.

I have two questions - if y is not equal to 4, what is the math rule that allows you to eliminate the two (y-4)s when they aren't set equal to 0?


if y is not 4, then (y - 4) is nonzero. so, you can divide both sides of the equation by (y - 4), in the same way that you could divide both sides by, say, 3 or 16 or 100.

Second - in the MGMAT explanation, once simplified, you get down to y+4 = x/2, but then the next step and answer is y = x-8/2. How do you get the 8? Shouldn't it be x/2-4?


again, the notation is somewhat ambiguous here, but i'll assume that the expressions are supposed to be (x - 8) / 2 and (x/2) - 4.

if those are the right expressions, then they are equivalent to each other.
in your expression (x/2) - 4, just make a common denominator:
x/2 - 8/2
then subtract the expressions, and you'll get the other expression.
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Re: If y is not equal to 4, x is not equal to 0...

by cschmidlapp Sat Jun 29, 2013 5:07 pm

Yes, your assumptions about the formats were correct. Sorry for any confusion and thanks for the help.
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Re: If y is not equal to 4, x is not equal to 0...

by RonPurewal Mon Jul 01, 2013 7:59 am

you're welcome
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Re: If y is not equal to 4, x is not equal to 0...

by steilbergauf Sun Dec 15, 2013 10:51 am

Hi guys,

can someone please help me out with the solution?!

I dont understand how you get from

(y+4)/3x = 6

to

y+4= x/2

Many thanks in advance!
RonPurewal
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Re: If y is not equal to 4, x is not equal to 0...

by RonPurewal Sun Dec 15, 2013 1:09 pm

steilbergauf Wrote:Hi guys,

can someone please help me out with the solution?!

I dont understand how you get from

(y+4)/3x = 6

to

y+4= x/2

Many thanks in advance!


If that's supposed to say (y + 4)/(3x) = 6, then you don't get that. In that case, you'd multiply by 3x on both sides, getting y + 4 = 18x.
Do you have a screen shot?
steilbergauf
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Re: If y is not equal to 4, x is not equal to 0...

by steilbergauf Sun Dec 15, 2013 1:28 pm

Hi Ron,

thanks for your quick reply. I probably just misinterpreted the following:
http://postimg.org/image/goezo8f5z/
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Re: If y is not equal to 4, x is not equal to 0...

by RonPurewal Tue Dec 17, 2013 2:31 am

Yeah -- the "6" doesn't magically migrate up to the top of the fraction. When you cancel the top of that fraction, you're left with 1/6, not 6.