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Let A and B be two sets with n(A) = 70, n(B) = 60, and n(A union B) = 110. Find n(A intersection B).
- 240
- 20
- 100
- 120
Correct answer: 20
Solution
By inclusion-exclusion: n(A intersection B) = n(A) + n(B) - n(A union B) = 70 + 60 - 110 = 20.
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