09/13/11 - Mixing Problems

			A tank initially holds 100 gal of pure water. At time t = 0, a solution containing salt at 2 lb/gal begins to enter the tank at the rate of 3 gal/min. At the same time a drain is opened at the bottom of the tank so that the volume of solution in the tank remains constant. Assuming the salt is uniformly distributed in the solution, how much salt is in the tank after 60 min?

			A 600-gal tank is filled with 300 gal of pure water. A spigot is opened above the tank and a solution containing salt at 1.5 lb/gal begins flowing into the tank at a rate of 3 gal/min. Simultaneously, a drain is opened at the bottom of the tank allowing the solution to leave the tank at a rate of 1 gal/min. Assuming uniform mixing, what will the salt content in the tank be when the volume is 600 gal?

			Consider two tanks, labeled A and B. Tank A has 100 gal of solution containing 20 lb of salt. Tank B has 200 gal of solution containing 40 lb of salt. Pure water flows into tank A at a rate of 5 gal/s. Solution leaves tank A through a drain at the bottom of tank A at a rate of 5 gal/s and flows immediately into tank B at the same rate. Solution leaves tank B through a drain at the bottom of tank B at a rate of 5 gal/s. What is the salt content of tank B after 1 min?