Total gasoline = 10 gallons
Gasoline left after 100 miles = 5 gallons
Gasoline used in 100 miles
= Total gasoline - Gasoline left after 100 miles
= 10 gallons - 5 gallons
= 5 gallons
Gasoline used in 1 mile
= Gasoline used in 100 miles/100
= 5 gallons/100
= 0.05 gallons
