Digital PSAT Math Practice Question 234: Answer and Explanation

Question: 234

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

• A. Cost = L²
• B.
• C.
• D.

Correct Answer: C

Explanation:

(C) You need to come up with an expression for the area of the wall, then recognize that it will cost $12 for every 60 square feet (paint costs $12 per gallon and one gallon covers 60 square feet).

You know that W = L and A = LW since the wall is a rectangle, so plugging in L for W, you get .

Multiplying the cost/area by the area will cancel area and leave you with cost: