I’ve had some statistics courses but why would I ever remember something like that at a time when I actually needed it.
If you’re in the same boat, here’s some refreshers to help along the way.
There’s a Probability textbook over at Google books.
The Subtraction Rule of Probability
The Addition Rule of Probability
The Multiplication Rule of Probability
There’s combinatorics and the associated permutations.
Oh, and a little on factorials.

This is just analysis right? Do we really need complicated analysis to figure it out or do we just need to understand the clues they left for us?
It’s mostly needed to prove how unlikely or likely something is. Take Gillogly’s skewering of the Beale ciphers for example, not possible without statistics and probability.
This looks like filler