PSAT Math Multiple-Choice Question 793: Answer and Explanation

Question: 793

A wall's height is two-thirds that of its length. The entire wall will be painted. The paint costs $12 per gallon, and 1 gallon of paint covers 60 square feet. What expression gives the cost of the paint (assuming one can purchase partial and full gallons) to cover a wall that is L feet long?

• A. Cost = L²
• B.
• C.
• D.

Correct Answer: C

Explanation:

(C) First, you need to come up with an expression for the area of the wall. Then recognize that paint will cost $12 for every 60 square feet (paint costs $12 per gallon and 1 gallon covers 60 square feet).
You know that and A = LW since the wall is a rectangle. Plugging in for W
gives .
Multiplying the cost/area by the area will cancel out the area and leave you with cost:

The answer is choice (C).