I. x + 2y + 3z = 2
II. x + y - z = 0
III. 2x + 2y - z = 1

What is the value of y in the system above?

(A) -2
(B) -1
(C) 0
(D) 1
(E) 2

is there an easier and quicker way to solve this question than my approach? this one took me around 6 minutes to solve, so i guess there must be an easier way.

my approach:

1. from the given system of equations i can make equation II. to be x + y = z

2. now put that in III. :

2x + 2y - (x + y) = 1

= 2x + 2y - x - y = 1

= x + y = 1

that gives us z = 1!

3. put z = 1 in I. and solve:

x + 2y + 3 = 2; calculate minus 3

= x + 2y = -1; calculate minus x

= 2y = -1 - x;

4. now put 2y = -1 - x in III. and solve:

2x + (-1 - x) - 1 = 1

= x - 2 = 1; calculate plus 2

that gives us x = 3

5. now solve for y with x = 3 and z = 1:

x + y = 1

= 3 + y = 1; calculate minus 3

that gives y = -2, and hence answer (A) -2

any quicker way?

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________