Complement

The complement of a set B, written B’, is the set of all the members of the universal set, which are not elements of the set B.

Example
If, U = {3, 5, 7, 9, 11, 13, 15, 17, 19}
And, B = {5, 11, 17, 19}
Then, B’ = {3, 7, 9, 13, 15}
Where, B’ is “the complement of B”.

Example- Using Venn diagram

Sets are represented by a drawing called a Venn diagram, in which a rectangle is used to represent a universal set, U, and circles inside the rectangle, used to represent subsets.

Using the example above, below is a Venn diagram showing B’.