What is the value of xy - yz?

[BTGModeratorVI]

What is the value of xy - yz?

(1) y = 2
(2) x - z = 5

Answer: C
Source: Official guide

[Brent@GMATPrepNow]

What is the value of xy - yz?

(1) y = 2
(2) x - z = 5

Answer: C
Source: Official guide

Important: Notice that we can take xy - yz and factor out the y to get the following equivalent expression: y(x - z)

Target question: What is the value of y(x - z)?

Statement 1: y = 2
Our goal is to determine the value of y(x - z)
We now know the value of y, but we don't know the value of (x - z)
Statement 1 is NOT SUFFICIENT

Statement 2: x - z = 5
Our goal is to determine the value of y(x - z)
We now know the value of (x - z), but we don't know the value of y
Statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that y = 2
Statement 2 tells us that x - z = 5
So, y(x - z) = 2(5) = 10
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent

[deloitte247]

To find the target question (i.e the value of xy - yz), we have to evaluate both statements' conditions.

Statement 1: y=2
There is no given value for x and z; this implies that we cannot estimate the value for xy-yz. So, therefore, statement 1 is NOT SUFFICIENT.

Statement 2: x-z=5
There is no given value for y; this implies that we cannot estimate the value for xy-yz. So, therefore, statement 2 is NOT SUFFICIENT.

Combining both statements:
From statement 1, y=2
From statement 2, x-z=5
xy - yz
y (x-z) = 2(5) = 10
Since this combination of both statements answers the target question, then it is SUFFICIENT.

The answer is, therefore, option C.