Why It's E?! Please Explain.

Haitham · Last edited by Haitham on Mon Dec 29, 2008 4:45 am; edited 1 time in total

Hi all!

I need help understanding this question and its answer:

If xy+z=x(y+z), which of 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

The correct answer is E, but why? (my first choice was A)

Thanks,
Haitham

cramya · Posted: Tue Nov 18, 2008 5:13 pm Post subject:

Haitham,
Refer to http://www.beatthegmat.com/gmatprep-xy-z-x-y-z-t18211.html

Stuart provided a nice solution with explanation which may answer your question.

Let us know if u still have questions.

Ossa · Posted: Tue Nov 18, 2008 6:13 pm Post subject: Re: Why It's E?! Please Explain.

Hi Haitham,

I think this is the shortest way to do it:

If xy+z=x(y+z), then
xy+z=xy+xz, which means that xz=z, and this can only happen if x=1, or if z=0.

Haitham · Posted: Wed Nov 19, 2008 7:48 am Post subject:

Thank you guys! It's all clear to me now Very Happy