(a) Suppose you have a bank account in which money grows at an annual rate of 3 percent.

If you have 10,000 dollars in the account, at what rate is your money growing?
Rate of change = dollars/year

Suppose that you are also withdrawing money from the account at $1,000 per year. What is the net rate of change in the amount of money in the account?
Rate of change = dollars/year

(b) Suppose that a water tank contains 100 gallons of salt water and that a salty solution, which contains 20 grams of salt in every gallon, enters the tank at 2 gallons per minute.

How much salt enters the tank each minute?
Rate of salt entering = grams/minute

Suppose that initially there are 300 grams of salt in the tank. How much salt is in each gallon at this point in time?
Concentration of salt = grams/gallon

Finally, suppose that evenly mixed solution is pumped out of the tank at the rate of 2 gallons per minute. At what rate is the salt leaving the tank?
Rate of salt leaving = grams/minute

What is the net rate of change in the amount of salt in the tank?
Rate of change = grams/minute