- #1

SithsNGiggles

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## Homework Statement

A tank holds 10 L of pure water. Brine (unknown constant concentration) is flowing into the tank at 1 L/min. The water is mixed well and drained at 1 L/min. After 20 min, there are 15 g of salt left in the tank. What is the concentration of the salt in the incoming brine?

## Homework Equations

## The Attempt at a Solution

Let A(t) = amount of salt (g) at time t (min).

I can see that A(20) = 15, but I'm confused on how I should set up the diff eq.

I know that A'(t) = (concentration of incoming * rate of incoming) - (concentration of outgoing * rate of outgoing)

I let

r = concentration of incoming

s = concentration of outgoing

so I think that gives mes = concentration of outgoing

##\dfrac{dA}{dt} = (r \frac{g}{L})(1 \frac{L}{min}) - (\frac{1}{10} s \frac{g}{L})(1 \frac{L}{min})##

##\dfrac{dA}{dt} = r - \frac{1}{10} s##

##\dfrac{dA}{dt} = r - \frac{1}{10} s##

But then I've no idea where to go from here.