A tank initially holds 80gal of a brine solution containing 1/8lb of salt per gallon. At t=0, another brine solution containing 1lb of salt per gallon is poured into the tank at the rate of 4gal/min, while the well stirred mixture leaves the tank at the rate of 8gal/min. Find the amount of salt in the tank when the tank contains exactly 40 gal of solution.

Question

A tank initially holds 80gal of a brine solution containing 1/8lb of salt per gallon.  At t=0, another brine solution containing 1lb of salt per gallon is poured into the tank at the rate of 4gal/min, while the well stirred mixture leaves the tank at the rate of 8gal/min.  Find the amount of salt in the tank when the tank contains exactly 40 gal of solution.

sriram · Answer

gallons of brine present in the tank=4t-8t=-4t  (4 gallons leave per minute)
40 gallons leave in10 mins

anonymous · Answer

Yes, I got that and then I used simple algebra to get an answer of 40 pounds of salt which was incorrect.

anonymous · Answer

u hav to use differential equations

anonymous · Answer

May someone please help me set this up?  This problem really has me stumped.