A family has two cars...

Question

A family has two cars. The first car has a fuel efficiency of 35 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 2600 miles, for a total gas consumption of 70 gallons. How many gallons were consumed by each of the two cars that week? 

Answer 1

35F + 40S = 2600

F +S = 70

35F +35S = 35(70) = 2450

subtract last equation from 1st to eliminate one variable

40S -35S = 2600 -2450

5S = 150

S= 150/5 = 30 mpg for the 2nd car

F =70-30 = 40 mpg for the 1st car

35(40) + 40(30 = 1400 + 1200 = 2600