A tank contains 200 L of fluid in which 30 grams of salt are dissolved. Brine containing 1 g of salt per liter is then pumped into the tank at a rate of 4L/min; the well mixed solution is pumped out at the same rate. Find the concentration of grams of salt in the tank after 30 minutes of the addition of brine.

The final concentration is 0.47 g/L.

Explanation:

Initial solution in the tank:

t = 0

m = 30g

V = 200 L

After 30 minutes (salt pumped into):

t = 30 min

m = 30 g + 30 min x 4g/min = 150g

V = 200 L + 30 min x 4 L/min = 320 L

c = 150 g / 320 L = 0.47 g/L

After 30 minutes (salt pumped out):

t = 30 min

m = 150 g - 30 min x 4Lx0.47g/min. L = 93.6g

V = 320 L 30 min x 4 L/min = 200 L

c = 93.6 g / 200 L = 0.47 g/L

Therefore, the final salt concentration will be 0.47 g/min.