Sum and product counting principles
Disjoint finite alternatives have total count equal to the sum of their counts.
Key knowledge
Disjoint finite alternatives have total count equal to the sum of their counts. Sequential choices with exactly nᵢ options at each stage for every earlier permitted choice have total count ∏nᵢ; in particular |A×B|=|A||B|.
Conditions and scope
- Alternatives must be disjoint for simple addition.
- The product requires the specified constant number of options, not an assumption that overlapping choices are independent.
Sources · 1
References
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Evidence and review
Section 1.1 additive and multiplicative principles, including Cartesian-product cardinality.
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Entry details
Permanent link to this entry ↗- Record identity
- math-counting-sum-product
- Revision
- university-core.1
- Structured reference record
- University core expansion