InclusionExclusion PrincipleLet A, B be any two finite sets. Then n (A ∪ B) = n (A) + n (B)  n (A ∩ B) Here "include" n (A) and n (B) and we "exclude" n (A ∩ B) Example 1:Suppose A, B, C are finite sets. Then A ∪ B ∪ C is finite and n (A ∪ B ∪ C) = n(A) + n(B) + n(C)  n(A ∩ B)  n(A ∩ C)  n(B ∩ C) + n(A ∩ B ∩ C) Example 2:In a town of 10000 families it was found that 40% of families buy newspaper A, 20% family buy newspaper B, 10% family buy newspaper C, 5% family buy newspaper A and B, 3% family buy newspaper B and C and 4% family buy newspaper A and C. If 2% family buy all the newspaper. Find the number of families which buy
Solution: 1. Number of families which buy all three newspapers: 2. Number of families which buy newspaper A only 3. Number of families which buy newspaper B only 4. Number of families which buy newspaper C only 5. Number of families which buy None of A, B, and C n (A ∪B ∪C)^{c} = 100  n (A ∪ B ∪ C) n (A ∪B ∪C)^{c} = 100  [40 + 20 + 10  5 3 4 + 2] n (A ∪B ∪C)^{c} = 100  60 = 40 % 6. Number of families which buy exactly only one newspaper 7. Number of families which buy newspaper A and B only 8. Number of families which buy newspaper B and C only 9. Number of families which buy newspaper C and A only 10. Number of families which buy at least two newspapers 11. Number of families which buy at most two newspapers 12. Number of families which buy exactly two newspapers
Next TopicMathematical Induction

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