Math questions from mba.com and GMAT Prep software
michalw623
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GMAT prep Problem- equations

by michalw623 Fri Apr 22, 2016 10:48 am

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
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Re: GMAT prep Problem- equations

by tim Sat Apr 23, 2016 8:50 pm

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

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RonPurewal
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Re: GMAT prep Problem- equations

by RonPurewal Sun Apr 24, 2016 5:21 am

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
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Re: GMAT prep Problem- equations

by adiagr Fri May 27, 2016 1:44 am

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
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Re: GMAT prep Problem- equations

by RonPurewal Wed Jun 01, 2016 3:08 am

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