Pregunta: Un gran tanque de 500 galones está lleno de agua pura. Le entra salmuera que tiene 2 lb de sal por galón a razón de 5 gal/min. La solución bien mezclada sale del tanque con la misma razón. Determine la cantidad A(t) de libras de sal que hay en el tanque al tiempo t.

To start answering this question, first understand that we are asked to find , which represents the amount of salt in the tank at any given time . According to the problem statement, the rate of change of salt in the tank can be represented by the difference between the rate at which salt enters the tank and the rate at which it leaves, i.e. . Let's first determine the rate of salt entering the tank, , using the information given. We know that the brine solution enters the tank at a rate of 5 gallons per minute and has a concentration of 2 pounds of salt per gallon, so the rate of salt entering is pounds per minute.