**1. Homework Statement**

A container has 10 pounds of salt dissolved in 100 liters of water. Pure water is pumped in at 4 L/hour and perfectly mixed solution is pumped out at 3L/hour.

How much salt remains in the tank after 2 hours?

**3. The Attempt at a Solution**

change in pounds of salt = pounds of salt divided by the ever growing amount of liters times the amount of liters leaving should equal the pounds of salt leaving.

[tex]

\frac{dP}{dt} = \frac{P}{100 + 4t}(-3)t

[/tex]

where P is a function for pounds of salt in terms of hours.

OR should the total volume be the difference of the liters entering and leaving? I thought it makes more sense to say the liters are added at 4L as 3L leave, so we should think of the total volume as increasing by 4L regardless of the 3L leaving.