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## Homework Statement

A rigid tank of volume "V" contains salt dissolved in water at a concentration "C". Fresh water flows into the tank at a rate of "F". A fraction "x" of the exit flow is recirculated back into the entrance flow.

**Given:**

V, Volume of tank

Fin, Flow rate in

Fo, Flow rate out

x, Fraction of volume flow-rate recirculated

Co, Initial concentration

C(t), Concentration in tank at time t

## Homework Equations

[tex]\frac{dC}{dt}=\text{concentration of salt entering}-\text{concentration of salt leaving}[/tex]

[tex]C_{in}=xFC(t)[/tex]

[tex]C_{out}=(1-x)FC(t)[/tex]

so [tex]\frac{dC}{dt}=xFC(t)-(1-x)FC(t)[/tex]

## The Attempt at a Solution

[tex]\frac{dC}{dt}=xFC(t)-(1-x)FC(t)[/tex]

When I plot this using Euler's Method, I get this graph. This is obviously incorrect, because it does not reflect exponential decay. Can someone help me out? I'm really not sure what I've done wrong.