Two mechanics worked on a car. The first mechanic worked for 15 hours, and the second mechanic worked for 5 hours. Together they charged a total of $1150 .

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
15
miles per gallon of gas. During one particular week, the two cars went a combined total of
925
miles, for a total gas consumption of
50
gallons. How many gallons were consumed by each of the two cars that week?

Answer 1

x=# gallons used by the 20 mpg car

y=# gallons used by the 15 mpg car

x+y=50

20x+15y=925

x+y=50

x=50-y

substitute

20(50-y)+15y=925

1000-20y+15y=925

1000-925=20y-15y

75=5y

y=75/5

y=15 gallons of gas used by the 15 mpg car

50-15=35 gallons used by the 20 mpg car

check: 15*15+35*20=225+700=925 miles