SOLUTION: if n(A U B)=60 ,n(A ∩ B)=40 ,and n(A)=n(B),find n(A)

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Question 480801: if n(A U B)=60 ,n(A ∩ B)=40 ,and n(A)=n(B),find n(A)
Answer by Tatiana_Stebko(1539) About Me  (Show Source):
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n(A U B)=n(A)+n(B)-n(A ∩ B)
If n(A)=n(B), then n(A U B)=2n(A)-n(A ∩ B)
60=2n(A)-40
2n(A)=60+40
2n(A)=100
n(A)=50