Joe deposits 10 today and another 30 in five years into a fund paying simple interest of
11% per year.
Tina will make the same two deposits, but the 10 will be deposited n years from today
and the 30 will be deposited 2n years from today. Tina’s deposits earn an annual
effective rate of 9.15% .
At the end of 10 years, the accumulated amount of Tina’s deposits equals the
accumulated amount of Joe’s deposits.

Joe’s accumulative value = 10[1 + 0.11(10)] + 30[1 + 0.11(5)] = 67.5
Tina’s accumulative value = 10(1.0915)10–n + 30(1.0915)10–2n = 10(1.0915)10 ◊ vn + 30(1.0915)10 ◊
v2n = 24vn + 72v2n .
72v2n + 24vn – 67.5 =
vn = 24 576 19, 440
144
− ± + = 0.8158
n ◊ ln[1/1.0915] = ln(0.8158) \ n = 2.33 .

对吗？
可是看到weekly 里面Joe’s accumulative value = 10[1 + 0.11(10)] + 30[1 + 0.11(10)]/(1 + 0.11(5)) = 61.645