Question

A family has two cars. The first car has a fuel efficiency of 20 miles per gallon of gas and the second has a fuel efficiency of 40 miles per gallon of gas. During one particular week, the two cars went a combined total of 1100 miles, for a total gas consumption of 35 gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

Car 1 consumed 15 gallons, and Car 2 consumed 20 gallons.

Explanation:

fuel efficiency = distance in miles/gallons of gas

fuel efficiency * gallons of gas = distance in miles

Car 1: 20 mpg

Car 2: 40 mpg

Total miles: 1100

Miles of Car 1: x

Miles of Car 2: 1100 - x

Total gallons: 35

Gallons for Car 1: y

Gallons for Car 2: 35 - y

Car 1:

fuel efficiency * gallons of gas = distance in miles

20 * y = x

Car 2:

fuel efficiency * gallons of gas = distance in miles

40 * (35 - y) = 1100 - x

20y = x

1400 - 40y = 1100 - x

20y = x

x = 40y - 300

40y - 300 = 20y

20y = 300

y = 15

35 - y = 35 - 15 = 20

Car 1 consumed 15 gallons, and Car 2 consumed 20 gallons.