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Why It's E?! Please Explain.

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by Haitham » Tue Nov 18, 2008 5:07 pm
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
Last edited by Haitham on Mon Dec 29, 2008 4:45 am, edited 1 time in total.
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by cramya » Tue Nov 18, 2008 5:13 pm
Haitham,
Refer to https://www.beatthegmat.com/gmatprep-xy- ... 18211.html

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

Let us know if u still have questions.
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Re: Why It's E?! Please Explain.

by Ossa » Tue Nov 18, 2008 6:13 pm
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 wrote: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 you,
Haitham
Ossa Elhadary, PhD, CISA, PMP
Math Specialist
Test Prep New York
maximize your score, minimize your stress

www.testprepny.com
[email protected]
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by Haitham » Wed Nov 19, 2008 7:48 am
Thank you guys! It's all clear to me now :D
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