Data Sufficiency

M7MBA wrote:Is y = 7?

(1) (x - 4) = 0
(2) (x - 3)(y - 7) = 0

Target question: Is y = 7?

Statement 1: (x - 4) = 0
This tells us that x = 4, but it provides no information about the value of y
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: (x - 3)(y - 7) = 0
This tells us that EITHER x = 3 OR y = 7
Consider the following cases:
Case a: x = 5 and y = 7. Notice that these values satisfy the equation, because we get (x - 3)(y - 7) = (5 - 3)(7 - 7) = 0. In this case, the answer to the target question is YES, y DOES equal 7
Case b: x = 3 and y = 4. Notice that these values satisfy the equation, because we get (x - 3)(y - 7) = (3 - 3)(4 - 7) = 0. In this case, the answer to the target question is NO, y does NOT equal 7
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x = 4
Statement 2 tells us that EITHER x = 3 OR y = 7
If x = 4, then it CANNOT be the case that x = 3, which means y MUST equal 7
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent