The worker pours salt into the 100 gal tank at the rate of 2 lb/min. Target is a 0.01 lb/gal concentration of salty water. Derive the equation which determines rate of change of concentration in time. Find how long worker should pour in salt to reach desired concentration.
Now assume worker pours in salt from the big bag at the rate which dies away exponentially. Specifically rate is 4 exp(-2t) lb/min. How long it will take to reach desired concentration?