Question

Luke is going to repaint both sides of the door of his room. The door is 36 inches long by 80 inches high. His options at the paint store are below. 1 gallon of paint costs $10 and covers 4,400 square inches of area. 12 gallon of paint costs $7 and covers 2,200 square inches of area. If the door requires 2 coats of paint, what is the minimum cost of painting the door of Luke's room?

Answer 1

$26.20 minimum cost of option 1
$36.68 minimum cost of option 2

Area₁ = Length x Width
A₁ = 80 x 36
A₁ = 2880 in²  * this in only one side of the door.

Total Area = A₁ x 2 sides = 2880 = 5760 in²  * only good for 1 coating of paint
Total Area to be coated = 5760 x 2 coats of paint = 11,520 in²

1st option - $10 / gallon  and 4400 sq. in.
2nd option - $ 7 / gallon and  2200 sq. in

11,520 / 4400 = 2.62 x $10 = $26.20 minimum cost of option 1
11,520 / 2200 = 5.24 x $  7 = $36.68 minimum cost of option 2