MathLiveRule of sum
If two sets are disjoint, the number of elements in their union equals the sum of their individual sizes. It is used to count outcomes that fall into mutually exclusive cases.
A\cap B = \emptyset \implies |A \cup B| = |A| + |B|What the symbols mean
| a finite set | |
| a finite set disjoint from A | |
| the union of A and B | |
| the cardinality (number of elements) of A |
About this formula
- FieldMathematics
- TopicCombinatorics
- LevelHigh school
- Also calledaddition principle, sum rule, rule of sum counting, disjoint union cardinality, counting disjoint sets, addition rule combinatorics
- SourceWikidata Q2360148
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