Question

Peter decides to mix grades of gasoline in his truck. He puts in 11 gallons of regular and 7 gallons of premium for a total cost of $76.99. If premium gasoline costs $0.25 more per gallon than regular, what was the price of each grade of gasoline?

Answer 1

11r + 7p = 76.99
p = r + 0.25

11r + 7(r + 0.25) = 76.99
11r + 7r + 1.75 = 76.99
18r = 76.99 - 1.75
18r = 75.24
r = 75.24/18
r = 4.18 <=== regular : $ 4.18 per gallon

p = r + 0.25
p = 4.18 + 0.25
p = 4.43 <=== premium : $ 4.43 per gallon