text: a car can pump 500 gallons of gas in 20 minutes. how much gas can a car pump in 30 minutes?   these are just similar ratios:  500 gallons / 20 minutes = x gallons / 30 minutes  500 / 20 = x / 30  now solve for x (you can cross multiply if you like): 20x = 15000 x = 750 gallons.  it's also rather intuitive to see that you got 500 gallons in 20 minutes.  so in 10 minutes more, you will pump half again as much.  500 + 250 = 750 gallons.