A tank contains 80 kg of salt and 2000 L of water. Pure water enters a tank at the rate 6 L/min. The solution is mixed and drains from the tank at the rate 3 L/min.

Question

Find the amount of salt in the tank after 1 hours.

Answer 1

note that dV/dt = 3-6 =-3 l/m thus V(t)=-3t+2000 Liters. Note that the concentration of salt = M/V and the reduction of salt = dM/dt=-3M/V ... solving yields dM/M=-3dt/(2000-3t) and M(t)=6.4E11/(3t+2000)³ and M(60)=61.8 Kg