Question

Mary has to fill the 15-gallon gasoline tank on her car. While she is filling the tank, she notices that it takes 15 seconds to pump one gallon of gasoline into the car. At this rate of change, what is the approximate number of minutes it will take Mary to fill the tank with gasoline?

Answer 1

Way 1:
seconds / gallons = 15 / 1 = x / 15
Cross multiply
x = 225
Way 2:
15 x 15 = 225 seconds
60 seconds in a minute so...
225/60 = 3.75
It will take Mary 3.75 minutes, approximately 4 minutes, to fill the tank with gasoline.