If $x is invested at a constant annually compound interest rate of k percent, what is the ratio of the total amount including interest after 4n years to that after 2n years?  Choose the most appropriate option:
A) (1+k)^n  B) (1+k/100)^2n  C) (1+kn/100)  D) (1+n/100)^k  E) (1+kn)
Amount after 4n years will be = x ( 1 + k/100)^4n   Amount after 3n years will be = x ( 1 + k/100)^2n   So, required ratio will be -   { x ( 1 + k/100)^4n } / {x ( 1 + k/100)^2n } = (1+k/100)^2n   Hence answer will be a. (1+k/100)^2n   (1+k/100)^2n
<result>B</result>
If $x is invested at a constant annually compound interest rate of k percent, what is the ratio of the total amount including interest after 4n years to that after 2n years?