api: "YAML JSON TOON Database" version: 1.0.0 format: json dataset: slug: combinatorics-fundamentals title: "Combinatorics Fundamentals" description: "Core counting principles and combinatorial formulas." category: Mathematics category_slug: mathematics tags: "math,combinatorics,counting,permutations,combinations" view_count: 0 data [7]{principle,description,formula}: "Product Rule","If task A has m ways and task B has n ways, both can be done in m * n ways.","m * n" "Sum Rule","If tasks are mutually exclusive with m and n ways, total is m + n.","m + n" Permutations,"Ordered arrangements of r elements from n items.","P(n,r) = n! / (n - r)!" Combinations,"Unordered selections of r elements from n items.","C(n,r) = n! / (r!(n-r)!)" "Permutations with Repetition","Arrangements when some elements are identical.","n! / (n1! * n2! * ... * nk!)" "Pigeonhole Principle","If n items are placed into m containers and n > m, some container has >= 2 items.",ceil(n/m) "Binomial Theorem","Expansion of (a + b)^n.","(a+b)^n = Sum C(n,k) * a^(n-k) * b^k"