This is a lecture of Khan Academy. Compound Interest and e (part 3)
Continuously compounding $P in principal at an annual interest rate of r for a year ends up with a final payment of $Pe^r

Benford's Law Explanation (Sequel to Mysteries of Benford's Law)
Vi and Sal talk through the intuition of Benford's law (part 2)

Precalculus

Source of these courses is khan
Non-trigonometry pre-calculus topics. Solid understanding of all of the topics in the "Algebra" playlist should make this playlist pretty digestible.
khan
Website: http://www.dnatube.com/school/khan