Mathematics - Discrete Mathematics - Combinatorics - Advanced Counting

10 steps: (1) MULTIPLICATION PRINCIPLE: if task 1 has m ways and task 2 has n ways (independent), total = m×n. (2) ADDITION PRINCIPLE: if method A has m ways OR method B has n ways (exclusive), total = m+n. (3) INCLUSION-EXCLUSION: |A∪B| = |A|+|B|-|A∩B|. For three: |A∪B∪C| = |A|+|B|+|C|-|A∩B|-|A∩C|-