A tank contains 200 liters of fluid in which 30 grams of salt is dissolved. Brine containing 2 grams of salt per liter is then pumped into the tank at a rate of 4 L/min. The well-mixed solution is pumped out at a slower rate of 3 L/min. Write a differential equation that models the amount of salt in the tank at any time.

Salt flows in at a rate of

(2 g/L) * (4 L/min) = 8 g/min

and out at a rate of

(B/(200 + t) g/L) * (3 L/min) = 3B/(200 + t) g/min

where B is the amount of salt in the tank at time t.

Then the net rate at which B changes is governed by the ODE,

Multipy both sides by :

Integrate both sides:

The tank starts with 30 g of salt, so B(0) = 30, which gives

pakistan's principal natural resources are arable land and water. about 25% of pakistan's agriculture accounts for about 21% [1] of gdp and employs about 43% of the labour force. in pakistan, the most agricultural province is punjab where wheat and cotton are the most grown.