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=1
4.x=1 or y=0
5.x=1 or z=0
OA is E
algebra
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The key word here is must.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
B. y = 1 and z = 0
D. x = 1 or y = 0
E. x = 1 or Z = 0
So, for example, consider answer choice A. While it's possible that x = 0 and z = 0, it need not be the case.
For example, x=1, y=1 and z=1 is another solution to the equation. So, this eliminates A.
The solution . . .
Given: xy+z = x(y+z)
Expand: xy+z = xy + xz
Subtract xy from both sides: z = xz
Rearrange: xz - z = 0
Factor: z(x-1) = 0
This tells us that z = 0 or x = 1
Answer: E
Cheers,
Brent
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Hi ash4gmat,
There's a discussion of this question here:
https://www.beatthegmat.com/must-be-true-qs-t278003.html
GMAT assassins aren't born, they're made,
Rich
There's a discussion of this question here:
https://www.beatthegmat.com/must-be-true-qs-t278003.html
GMAT assassins aren't born, they're made,
Rich
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We are given the following equation, which we can simplify:ash4gmat wrote: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=1
4.x=1 or y=0
5.x=1 or z=0
OA is E
xy + z = x(y + z)
xy + z = xy + xz
z = xz
z - xz = 0
z(1 - x) = 0
z = 0
or
1 - x = 0
x = 1
So x = 1 or z = 0
Answer:E
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xy + z = xy + xz
z = xz
0 = xz - z
0 = z * (x - 1)
so z = 0 or (x - 1) = 0, giving z = 0 or x = 1.
z = xz
0 = xz - z
0 = z * (x - 1)
so z = 0 or (x - 1) = 0, giving z = 0 or x = 1.