In order to answer a question about the probability of tossing a certain number of heads, we need to determine how many combinations of results would have at least a specific amount of heads. It is noted that relying on one variable for an estimate will have a larger margin of error compared to using multiple variables. Given that one in every 1000 items is defective, the probability of six items in a batch of 3000 being defective can be calculated. A new chapter on multidimensional Brownian motion and its relationship to PDEs has been added, along with a proof of Itô's formula. Using the binomial probability formula, the probability of a single bulb not being defective can be found. Chapter 7 discusses how data can be used to estimate parameters of interest. Chapter 3 discusses conditional probability and independence of events, which are important concepts when computing probabilities.