Let A and B be two sets such that : n (A) = 20, n (A ∪ B) = 42 and n (A ∩ B) = 4. Find
n (B)
We know,
n (A ∪ B) = n(A) + n(B) – n (A ∩ B)
Substituting the values we get
42 = 20+ n (B) – 4
42 = 16+ n (B)
n (B) =26