Another differential equation

Hello

We got a container holding 100 liters of saltwater (concentration: 1%).

We pour 5 liters/min saltwater (2% conc.) and remove 5 liters/min of the liquid in the tank.

The concentration of salt is the same in all of the container.

**When is the concentration 1.5%?**

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Ok I have nearly solved this problem, some details that don't fit in though.

My (near) solution:

Some trivial facts:

where y(t) is the amount of salt at a specific time.

We get this equation:

Solve it...

Well I think that I got it wrong somewhere, the above equation doesn't seem to fit.

Thanks for your replies.