This one varies a lot. Where I tutor in West LA & Santa Monica, it seems like public schools tend to put Probability and Sequences in Algebra 2, while private schools put it in Pre-Calc or Math Analysis, or they save it for AP Stats. For all I know, maybe your school puts this in Geometry. The one thing I do know is that this stuff is on the SAT, and that if you haven't already studied combination notation, you might want to give that a gander before trying the Binomial Probability video below.

Intro to Probability (SAT style)

In this video we'll learn what probability is, as well as a bunch of vocab words like "compound", "dependent", and "mutually exclusive". We'll also work a bunch of common examples, starting with colored marbles in a bag (with and without replacement), then moving on to coin tosses and dice.

Binomial Probability Formula

Finally, all that work on combinations will pay off (as if it hadn't already) when you get to use your nCr knowledge again, finding such amazing probabilities as: "In a family with 8 kids, what's the chance at least 2 are boys" and "If you flip a weighted coin 5 times, what's the probability of getting exactly 4 heads?"