SAT Mathematics Practice Test 3

The painter’s fee is given by $\mathit{n}\mathit{K}\mathit{l}\mathit{h}$, where n is the number of walls, K is a constant with units of dollars per square foot, $\mathit{l}$ is the length of each wall in feet, and h is the height of each wall in feet.
Examining this equation shows that $\mathit{l}$ and h will be used to determine the area of each wall.The variable n is the number of walls, so $\mathit{n}$ times the area of the walls will give the amount of area that will need to be painted.
The only remaining variable is $\mathit{K}$, which represents the cost per square foot and is determined by the painter’s time and the price of paint. Therefore, $\mathit{K}$ is the only factor that will change if the customer asks for a more expensive brand of paint.
Choice A is incorrect because a more expensive brand of paint would not cause the height of each wall to change. Choice B is incorrect because a more expensive brand of paint would not cause the length of each wall to change. Choice D is incorrect because a more expensive brand of paint would not cause the number of walls to change.