Question

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 35 miles per gallon of gas. during one particular week, the two cars went a combined total of 1975 miles, for a total gas consumption of 60 gallons. how many gallons were consumed by each of the two cars that week?

Answer 1

X : the gas used by first car in 1 particular week
y : the gas used by second car in 1 particular week
$x + y = 60 \\ x = 60 - y$
$30x + 35y = 1975 \\ 30 \times (60 - y) + 35y = 1975 \\ ... \\ y = 35 \\ x = 60 - y = 60 - 35 = 25$