(Q9). If A = {1, 2, 3,4,5}; B = {2,4,6,8} then find n(A∪B).

The set A contains five elements ∴ n(A) =

and the set B contains four elements ∴ n(B) =

But A∪B={,,,,,,} does not contain 9 elements and it contains 7 elements only.