Formulas
P(event) = Favourable outcomes / Total outcomes
nPr = n! / (n−r)! nCr = n! / (r! × (n−r)!)
P(A and B) = P(A) × P(B) (independent)
P(A or B) = P(A) + P(B) − P(A and B)
P(A or B) = P(A) + P(B) − P(A and B)
FAQ
What is the difference between permutation and combination?
Permutation counts arrangements where order matters (e.g., lock combinations). Combination counts selections where order doesn't matter (e.g., choosing team members). nPr ≥ nCr always.