How long will it take to empty the tank at 3000 if the time required to empty a tank varies inversely as the rate of pumping and a pump can empty the tank in 90 minutes at the rate of 1200 L per min?

To find the time to empty the tank at 3000 L, we use the formula ( T = k/r ) where T is the time, r is the rate of pumping, and k is a constant. Given that a pump empties the tank in 90 minutes at the rate of 1200 L/min, we can find k = Tr = 901200 = 108000. When pumping at a rate of 3000 L/min, the time taken to empty the tank is T = 108000/3000 = 36 minutes.