A geometrically increasing series of 20 end of year payments is deposited to fund an account. The first payment is $20,000, the geometric factor is 4%. The account is used for retirement purposes and will produce 30 consecutive annual payments of $60,000, starting at the end of year 16. Calculate the interest rate necessary to create this cash flow.
If the $60,000 payments start at the same point, but go on forever, what is the interest rate?