Suppose that when you were one year old, your grandmother gave you a shiny silver dollar. Your parents put that silver dollar in a savings account with a guaranteed 9% interest rate, and then promptly forgot about it.
a. Use the "Rule of 72" to estimate how much that account will grow to by the time you are 65.
b. Calculate exactly how much you will have in that account using the formula for compound interest.
c. How close are your answers to (a) and (b)?