The bedrock is that slab of solid rock that serves as the foundation for a large mass that rests on it. The formation remains for eons because the bedrock itself remains. The idea is important both to geology and engineering.
Before going to far, I'm going to take a moment to brag on an endorsement. My friend and professional poker player Andrew Breese (who earned a degree in statistics) said he learned something from the videos in the first two parts of this series. He is a smart guy, to be sure. This also means that a student like Antonio is capable of learning things after a decade off of learning math that an applied math professional did not get in his education. I hope this fact is appreciated by many viewers.
The bedrock in which Antonio and I worked on our fifth week/hour is that of combinations. Combinations are ubiquitous in counting/combinatorics, probability, and statistics. The binomial distribution (discrete version of the normal distribution/bell curve/Gaussian distribution) is based on combinations, and binomial/normal distributions are the most common distributions we find among real world phenomena, save possibly for the simple uniform distributions.
As usual, Antonio makes substantial progress---sometimes while taking his time to fully understand what is going on in the math.