Here are two links to questions (and their answers) in the Dr. Math archives.
Probability in Flipping Coins (Kay)
Six pennies are flipped. What is the probability of getting two heads and four tails? Etc.
Combinatorics Basics (Scamacca)
I need to prove that n chooses n-1 = n; e.g. C(n,n-1) = n.