Initally, a 100-liter tank contains a salt solution with concentration 0.5 kg/liter. A fresher solution with concentration 0.1 kg/liter flows into the tank at the rate of 4 liters/min. The contents of the tank are kept well-stirred, and the mixture flows out at the same rate it flows in. For the questions below, we measure t in minutes.

Determine the concentration (in kg/L) in the tank as a function of t time .

Question

Initally, a 100-liter tank contains a salt solution with concentration 0.5 kg/liter. A fresher solution with concentration 0.1 kg/liter flows into the tank at the rate of 4 liters/min. The contents of the tank are kept well-stirred, and the mixture flows out at the same rate it flows in. For the questions below, we measure  t in minutes.

Determine the concentration  (in kg/L) in the tank as a function of t time .

anonymous · Answer

x' = flow in - flow out

x'/100 = concentration at t

I figured that out minutes after asking :p

dumbcow · Answer

this took me awhile but i think i got it
C(t) = (50+0.4t)/(100+4t)
this came from 
the salt coming in was 0.1*4t
salt going out was C(t)*4t
net salt = C(t)*4t - 0.1*4t
initial salt content = 50
C(t) = (50 - net salt)/100