You made an investment of $16,500 into an account that paid you an annual interest rate of 2.8 percent for the first 7 years and 7.2 percent for the next 14 years. What was your annual rate of return over the entire 21 years

0.05712790 or 5.71%

Explanation:

Annual rate of return = [ (1 + r1) ^n1 x (1 + r2) ^n2]^[1 / (n1 + n2) ] - 1

n1 is the time period in which annual interest rate = 2.8%

n2 is the time period in which annual interest rate = 7.2%

So, n1 = 7 years and n2 = 14 years

= [ (1+2.8%) ^7 x (1+7.2%) ^14]^[1 / (7 + 14) ] - 1

= (1.21325420 x 2.64683577) ^ 1 / 21 - 1

= 1.05712790 - 1

= 0.05712790 or 5.71%