Question

A family has two cars. The first car has a fuel efficiency of 40 miles per gallon of gas and the second has a fuel efficiency of 30 miles per gallon of gas. During one particular week, the two cars went a combined total of 1250 miles, for a total gas consumption of 35 gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

let distance covered by the 40 mpg car be x miles
let the distance covered by the 30 mpg car be 1250-x
miles

gas used by the 40 mpg car = x/40
gas used by the 30 mpg car = (1250-x)/30

x/40 + (1250-x)/30 = 35
times 120
3x + 4(1250-x) = 4200
-x = -800
x = 800

So the more efficient car went 800 miles and used 20 gallons
the other car went 1250-800 or 450 miles and used 15 gallons