Probability Formulas
P(A): Favorable / Total outcomes
P(A and B): P(A) × P(B) [independent]
P(A or B): P(A) + P(B) − P(A and B)
C(n,r): n! / (r! × (n−r)!)
P(n,r): n! / (n−r)!
Frequently Asked Questions
What's the difference between combinations and permutations? Combinations don't care about order (choosing a team). Permutations do care about order (assigning positions).
What does "independent" mean? Two events are independent if one doesn't affect the other's probability. Coin flips are independent; drawing cards without replacement are not.