A = {1, 2, 3, 5, 7, 9, 11, 13}

B = {1, 2, 4, 6, 8, 12, 13}

A ∪ B = {1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13}

A ∩ B= {1, 2, 13}

n(A) = 8, n(B) = 7,

n(A ∪ B) = 12, n(A ∩ B) = 3

n(A ∩ B) = 12 …**(i) **

n(A) + n(B) – n(A ∩ B) = 8 + 7 – 3 = 12 …**(ii)**

∴ n(A ∪ B) = n(A) + n(B) – n(A ∩ B) … **[From (i) and (ii)]**