Mixing. Suppose a brine containing 0.3 kilogram (kg) of salt per liter (L) runs into...

Mixing. Suppose a brine containing 0.3 kilogram (kg) of salt per liter (L) runs into a tank initially filled with 400 L of water containing 2 kg of salt. If the brine enters at 10 L/min, the mixture is kept uniform by stirring, and the mixture flows out at the same rate. Find the mass of salt in the tank after 10 min (see Figure 2.4). [Hint: Let A denote the number of kilograms of salt in the tank at t min after the process begins and use the fact that

rate of increase in A = rate of input - rate of exit.

A further discussion of mixing problems is given in Section 3.2.]