When do I use n(A∪B) = n(A) + n(B) − n(A∩B) in Sets & Statistics, and what does it mean?
inclusion–exclusion for two sets.
n(A∪B) = n(A) + n(B) − n(A∩B) — inclusion–exclusion for two sets. Use it when: counting elements in either set. Always check the condition holds before plugging in numbers.
Key point
n(A∪B) = n(A) + n(B) − n(A∩B)
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