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# If xy+z=x(y+z), which of the following must be true? 1. x=0

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VP
Joined: 22 Nov 2007
Posts: 1079
If xy+z=x(y+z), which of the following must be true? 1. x=0 [#permalink]

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26 Dec 2007, 09:28
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If xy+z=x(y+z), which of the following must be true?

1. x=0 and z=0
2. x=1 and y=1
3. y=1 and z=0
4. x=1 or y=0
5. x=1 or z=0

OA is 5 and it's ok..but why not 1. also??
Director
Joined: 12 Jul 2007
Posts: 858

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26 Dec 2007, 10:43
xy+z = x(y+z) multiply through
xy+z = xy+xz subtract out
z=xz

for this to be true x must be equal to 1 (to get z=z) OR z equal to 0 (to get 0=0)

It says which one MUST be true. and while 1 works, it doesn't HAVE to be true because there are other alternatives (shown above)

the OA is correct
26 Dec 2007, 10:43
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