MrWallSt wrote:

If the ratio of x to y is 2 to 5, then (y-x)/(x+y)?

A. -7/3

B. -3/7

C. 3/7

D. 1

E. 7/3

Can any one solve this using algebra and not plugging in?

Dear

MrWallSt,

I'm happy to respond.

With all due respect, I believe the short answer to your question is simply "

no." This is a very straightforward question, very easy, designed as a simple plug-in question by the test author. Plugging in is the ideal way to approach this problem. I know lots of algebra, through multivariable calculus, and it's really somewhat beyond me what algebra one would use to approach this. I honestly think that no one skilled in mathematics would want to bring the machinery of algebra anywhere near this problem.

Your very question makes me suspicious. Yes, algebra is awfully useful in a large number of problems, but it is unreasonable to think that algebra can be used in

every single problem. It is highly unfruitful to see the letter x and immediately leap to algebra: that is precisely the kind of trap that GMAT writers design to ensnare students! If you routinely think this way, that mindset is an addiction to algebra and this addiction definitely will drag down your GMAT Quant score if you don't manage it.

The GMAT Quant section will always keep you on your toes. There's nothing you can memorize, no fixed set of rules, that will give you success every day. As soon as the GMAT writers realize that a large number of test-takers are using one fixed approach, they start writing problems designed to frustrate folks who are too attached to their rigid method. If you can't maintain mental agility, the GMAT will punish you. Here's an article about the type of thinking the GMAT demands:

http://magoosh.com/gmat/2013/mathematic ... -the-gmat/I hope this wasn't too emphatic a response. You may not be an "algebra addict" at all, but I have met many of them preparing for the GMAT, and I like to warn students of this danger.

I hope all this helps.

Mike

_________________

Mike McGarry

Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)