If A and B are two sets such than n(A) = 8, n(B) = 11 and n(A ∪ B) = 14 then find n(A ∩ B).

Given: n(A) = 8, n(B) = 11, n(A ∪ B) = 14
We know that n(A ∪ B) = n(A) + n(B) – n(A ∩ B)
⇒ 14 = 8 + 11 – n(A ∩ B)
⇒ 14 = 19 – n(A ∩ B)
⇒ n(A ∩ B) = 19 – 14
⇒ n(A ∩ B) = 5
Hence n(A ∩ B) = 5