Probability distributions in combinatorics context: Binomial distribution for P(X=k) = C(n,k) p^k (1-p)^(n-k) when selecting from two categories. Multinomial distribution: Extension to multiple categories. Problem applications: Distributing identical/distinct objects into groups with constraints. Example: 10 balls (7 red, 3 blue) distributed into 3 boxes. Use combinations with constraints. Exam tip: Recognize when distribution formulas apply. Connect to permutations/combinations conceptually. Practice: Real-world distribution problems (defective items, voting outcomes).