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Re: confusing Question from GMAT Prep test [#permalink]
26 Aug 2010, 04:24
This post received KUDOS
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
xy+z=x(y+z) --> xy+z=xy+xz --> xy cancels out --> xz-z=0 --> z(x-1)=0 --> either z=0 (in this case x can take ANY value) OR x=1 (in this case z can take ANY value).
To elaborate more: As the expression with y cancels out, we can say that given expression xy+z=x(y+z) does not depend on value of y. Which means that y can take ANY value. So all answer choices which specify the exact value of y are wrong.
Next: "AND" in answer choices means that BOTH values must be true, but "OR" in answer choices means that EITHER value must be true.
Re: If XY+Z=X(Y+Z), which of the following must be true ? [#permalink]
04 Feb 2014, 18:15
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