1 A book reviewer estimates that the probability that he receives a delivery of books to review on any one weekday is 0.1 . The first weekday in September on which he receives a delivery of books to review is the \(X\) th weekday of September.

1. State an assumption needed for \(X\) to be well modelled by a geometric distribution.
2. Find \(\mathrm { P } ( X = 11 )\).
3. Find \(\mathrm { P } ( X \leqslant 8 )\).
4. Find \(\operatorname { Var } ( X )\).
5. Give a reason why a geometric distribution might not be an appropriate model for the first weekday in a calendar year on which the reviewer receives a delivery of books to review.