Data Sufficiency

VJesus12 wrote:If y + 40x + 2 = 0, what is the value of xy?

(1) 16x = -4y + 28

(2) 13y = 91 - 52x

Target question: What is the value of xy?

Given: y + 40x + 2 = 0
Rearrange to get: 40x + y = -2

IMPORTANT: We are given one linear equation. If we given a different linear equation, then we can be certain to solve the system of equations for x and y, which means we can determine the value of xy
So, we need only determine whether each statement provides a linear equation that is different from the given linear equation (40x + y = -2)

Statement 1: 16x = -4y + 28
Divide both sides by 4 to get: 4x = -y + 7
Add y to both sides: 4x + y = 7
This second linear equation is different from the given linear equation (40x + y = -2
This means we COULD solve the system of equations for x and y, which means we COULD determine the value of xy
Since we COULD answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: 13y = 91 - 52x
Divide both sides by 13 to get: y = 7 - 4x
Add 4x to both sides: 4x + y = 7
This is the same equation that we have in statement 1.
So, if statement 1 is sufficient, we can also be certain that statement 2 is SUFFICIENT

Answer: D

Cheers,
Brent