CAT EXAM QUESTION

[KellyMSinclair]

This is a problem from the CAT exam.

If 3x - 3y = 12z, what is the value of x?

(1) 4z = 2 + y

(2) 4z = 6 - y

Apparently the answer is B (2) alone is sufficient, however I was also able to solve for (1). I rephrased the problem to be x-y=4z. I then substituted 2+y=4z into the question stem, so x-y= 2+y. Then I solved for y and got y=(x-2)/2 then plugged this back in to the problem and got x=-2. Did I solve this incorrectly?

[RonPurewal]

This is a problem from the CAT exam.

If 3x - 3y = 12z, what is the value of x?

(1) 4z = 2 + y

(2) 4z = 6 - y

Apparently the answer is B (2) alone is sufficient, however I was also able to solve for (1). I rephrased the problem to be x-y=4z. I then substituted 2+y=4z into the question stem, so x-y= 2+y. Then I solved for y and got y=(x-2)/2 then plugged this back in to the problem and got x=-2. Did I solve this incorrectly?

What did you "plug back into"? That's the key here.

Whatever it was, it shouldn't have given a solution for x. If you plug back into either of the available equations, you should get an equation with the same thing on both sides (thus no help).