GMAT prep Problem- equations

[michalw623]

GMAT prep Problem, from the official Gmat prep

If XY + Z = x(Y+Z) which f the following must be true


A. X=0 and Z=0

B. X=1 and Y=1

C. Y=1 and Z=0

D. X=1 or Y=0

E. X=1 or Z=0

I Checked the answers and both b and C must be true, which obviously cant be...

B- 1 +Z = 1 + Z
C. X +0 = X+ 0

Where am I wrong???

Thanks

[tim]

You've ignored the word "must" in the question. By your logic all five answer choices would be correct (try it yourself!).

[RonPurewal]

yeah... "must be true" DOES NOT mean "if you plug it in, it works".

"must be true" means "it's IMPOSSIBLE for this to be FALSE".

[adiagr]

Given: XY + Z = X(Y+Z)

Let us expand:

XY+ Z = XY+ XZ

XY cancels out.

Z = XZ

or XZ-Z= 0
Z*(X-1) = 0

so either Z=0 or X = 1

(E) is the answer.

[RonPurewal]

adiagr—hi, do you have a question? (this discussion has been dormant for more than a month)