The exercise says that there's a course that takes 3 years and the retention tax is affected by an uncertainty that is called $\epsilon_{i}$, and $\epsilon_{i}\sim N\left(0, \frac{0.15^2}{i}\right)$. After that we are supposed to determine the total number of students in the course during the first $20$ years. The "only" thing that I don't understand is how to discover $\epsilon$ and what to do with that... I mean, what's the proposal of knowing $N\left(0,\frac{0.15^2}{i}\right)$?
Thanks in advance.
Note: It is supposed to be done in Python