A.

we know, x = y+z

1) (x-y)^2 = 3^2
or (x-y) = 3
x = y+3
so z=3

2) (x+y)^2 = 15^2
or x+y=15
insufficient.
_________________

Hi sabineodf,

Many Quant questions on Test Day are pattern-based, so instead of looking at a prompt and thinking "what is this?", try thinking "what does this REMIND ME of?" In that way, you'll probably be less intimidated by the structure of the questions.

The prompt is worded in a 'quirky' way, but the information isn't that complex. From the two Facts, you should recognize that we're meant to be thinking about Classic Quadratics. If you're familiar with the 3 Classic Quadratics, then the bulk of the work in this question is just about re-writing information (and not about hard-core math skills).

For example, you are expected to know that....

X^2 -2XY + Y^2 can be re-written as....

(X-Y)(X-Y) =

(X-Y)^2

If you're not familiar enough with those ideas/rules yet, then that's okay, but you DO have to have to become familiar and practice them. Algebra is a BIG category in the Quant section, so you have to make sure that you're familiar enough with the broad concepts (and can do the specific calculations when required).

GMAT assassins aren't born, they're made,
Rich
_________________

This question is just testing quadratic templates

St 1

(x-y)(x-y) =9

Since this question is basically asking for the difference between a certain amount of people the answer can't necessarily be negative so x-y =2

suff

St 2

(x +y)(x+y) =225

insuff

A