Question

A farmer pumps water from an irrigation well to water his field. The time it takes to water the field varies inversely with the rate at which the pump operates. It takes 20 hours to water the field when the pumping rate is 600 litres per minute. If he adjusts the pump so that it pumps at a rate of 400 litres per minute , how long will it take to water the field ?

Answer 1

water required to irrigate the field is 600*60*20.  now the time takes to pump the required water at the rate of 400 liters per minute is 720000/24000 i.e 30 hours.