A family has two cars. The first car has a fuel efficiency of 30 miles per gallon of gas and the second has a fuel efficiency of 20 miles per gallon of gas. During one particular week, the two cars went a combined total of 1500 miles, for a total gas consumption of 55 gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

f = 1st car gallons , s = 2nd car gallons

f + s = 55 ... 20 f + 20 s = 1100

30 f + 20 s = 1500

subtracting equations (to eliminate s) ... 10 f = 400

solve for f , then substitute back to find s