Question

RM 350 was saved every month for 5 years in an account that pays 6% compounded monthly.
Calculate the accumulated amount if the interest rate was changed to 8% compounded monthly
after 2 years.

Answer 1

amount of the first annuity after 2 years
= 350(1.005^24 - 1)/.005

value of that amount at the end of another 3 years
= 350(1.005^24 - 1 )/.005 * (1.006666..)^36 <---- new rate for last 3 years
= ..... (part A)

amount of the 2nd annuity
= 350(1.006666...^36 - 1)/.00666...
= ..... (part B)

add parts A and B

there are many way to do this, another would be to set the "focal date" at the
end of two years , find the amount of the first annuity and the present value of the 2nd
add them up, then "move" it to the end of 3 years with (1.00666..)^36