word equations algebra

Question

A family has two cars. During one particular week, the first car consumed 20 gallons of gas and the second consumed 15 gallons of gas. The two cars drove a combined total of 725 miles, and the sum of their fuel efficiencies was 40 miles per gallon. What were the fuel efficiencies of each of the cars that week?

Answer 1

725 miles total for both cars

one uses 20 gallons, the other 15 gallons

combined mpg is 40

what is the mpg for each car?

Car A gets x miles per gallon

Car B gets 40-x miles per gallon

725 = 15x + 20(40-x)

5x = 800-725 = 75

x =75/5 = 15 mpg for the car that used 15 gallons

40-15 = 25 mpg for the car that used 20 gallons