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GPREP (Properties of Numbers)

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by zagcollins » Mon Jul 28, 2008 2:47 am
If xy+z=x(y+z), which of the following must be true?

A.x=0,z=0,
B.x=1,z=1
C.y=1 and z=0
D.x=1 or y=0
E.x=1 or z=0


OA Is E...
Last edited by zagcollins on Mon Jul 28, 2008 6:13 am, edited 1 time in total.
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by sudhir3127 » Mon Jul 28, 2008 2:55 am
IMO A
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by warlock » Mon Jul 28, 2008 3:02 am
xy+z = x(y+z)

xy+z = xy+xz

z = xz

z-xz = 0

z(1-x) = 0

this means z=0 or (1-x) = 0

meaning z = 0 or x = 1.

so i guess the ans is option E.
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by ricky » Mon Jul 28, 2008 3:04 am
IMO E..What is OA?
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by parallel_chase » Mon Jul 28, 2008 3:08 am
E absolutely. Whats the OA?
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by sudhir3127 » Mon Jul 28, 2008 3:21 am
Do we need to solve the eauation and find the values of X, y, z or the question mean for what values of X, y , Z the equation will be always true..

I understood it as the later one.. hence i opted for Zero, bcoz if its ) the LHS = RHS.. and will always hold true...
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by parallel_chase » Mon Jul 28, 2008 3:29 am
sudhir3127 wrote:Do we need to solve the eauation and find the values of X, y, z or the question mean for what values of X, y , Z the equation will be always true..

I understood it as the later one.. hence i opted for Zero, bcoz if its ) the LHS = RHS.. and will always hold true...
Well if you go by that way even the second option would hold true, x=1,z=1

xy+z=x(y+z)

y+1=y+1

On GMAT you cannot have 2 right answers, therefore option E is the correct.

I hope its clear.
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