Suppose you are calculating a present worth or future worth of a particular investment cash flow pattern with payments every month evaluated over the next 9 year. The interest rate on this account is 8% APR compounded monthly for the first 6 years and 10% APR compounded monthly for the last 3 years. Regarding the interest rate you will need to use when calculating present or future worth... you will need to calculate an effective monthly interest rate for the first 6 years with 8% APR and an effective monthly interest rate for years 7 through 9 with 10% APR and use these interest rates within those specific years in your analysis. you will calculate the average, which is 9% APR in this example, and use that in all calculations