Consider the two tanks shown in the figure below. Each has a capacity of 300 gallons. At time t = 0, tank 1 contains 100 gallons of a brine solution and tank 2 contains 200 gallons of a brine solution. Each tank also initially contains 50 pounds of salt. Pure water flows into tank 1, then a well-mixed solution flows out from tank 1 into tank 2. Finally, a well-mixed solution drains out of tank 2. The three flow rates indicated in the figure are each 10 gallons per minute.
Tank 1 capacity = 300 gallons
Volume of brine = 100 gallons
Amount of salt (lbs) = 50 lbs
Tank 2 capacity = 300 gallons
Volume of brine = 200 gallons
Amount of salt (lbs) = 50 lbs
(a) Write a system of differential equations that describes the amount of salt, x(t), in tank 1 and the amount of salt, y(t), in tank 2. Use the variables x and y below. Do not use x'(t) and y'(t).
(b) Solve the system to find formulas for x(t) and y(t). Write your answers in terms of the variable t.
(c) Explain what happens to the concentration of salt in each of the tanks. Justify your answer in a few sentences.