Permutations and Combinations

Khan Academy:
 * Permutations
 * Combinations
 * Permutations and Combinations 1
 * Permutations and Combinations 2
 * Permutations and Combinations 3
 * Permutations and Combinations 4
 * Probability using Combinations
 * Probability and Combinations (part 2)
 * Conditional Probability and Combinations

MIT 18.440

http://www.numericana.com/answer/counting.htm

http://en.wikibooks.org/wiki/High_School_Mathematics_Extensions/Discrete_Probability