Q4 of 71 Page 30

If n(A ∩ B) = 5, n(A ∪ B) = 35, n(A) = 13, find n(B).

Given, n(A ∩ B) = 5, n(A ∪ B) = 35, n(A) = 13


We have, n(A ∪ B) = n(A) + n(B) – n(A ∩ B)


35 = 13 + n(B) – 5


n(B) = 35 + 5 – 13 = 40 – 13 = 17


So, n(B) = 17


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