Afarmer 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 gallons per minute. if he adjusts the pump so that it pumps at a rate of 400 gallons per minute, how long will it take to water the field?

In order to answer this question, we use the concept of ratio and proportion wherein we use the equation,
                                 R1 / T2 = R2 / T1
where R is for rate and T is for time. Substituting the known values to the equation,
                                 (600)/x = (400)/ 20
The value of x from the equation is 30. Thus, it will take 30 hours if the rate was adjusted to 400 gallons per minute. 

What’s the equation you are trying to solve to get x?