# Definition, sets of objects and numbers

Sets are collections of well-defined objects of the same kind. In our daily lives, we often talk about a collection of objects or groups of objects or numbers. For instance, a team of players, a collection of flowers, and a group of students.

## Sets Notation

Mathematical, a set is often denoted or represented by a Capital letter. For example, F, G, A, B, Z, etc, and the members or elements of the set are enclosed in a curly bracket { }. So, if 4 is a member of set A, then we say A={4}.

## Elements or Members of sets

Elements or members of sets are objects or components of a set. For example, B = {3,6,9,12,15}, then 3,12,6,15,9 are all elements or members of set B. i.e 3 ∈ B. Also all the elements in set ∈ B. In mathematics, the symbol **∈** “means belongs” to or is a “member of”.

We can also say that 5 ∉ B and 10 ∉ B. In mathematics, the symbol ∉ means “not belong to”

The number of elements or members in a particular set is denoted by n(A). For example A={1,3,5,7,9}. The number of elements in the set is n(A)=5.

Let’s look at some examples under sets

Example: if Q= {2,4,6,8,10,12,14,16,18,20} and B={1,3,5,7,9,11,13,15,17,19} complete the following statements by inserting ∈ or** ∉.**

a) 8…..Q

b) 5….B

c)11….Q

d)20…B

answer: a) 8 ∈ Q

b) 5 ∈ B

c) 11 ∉ Q

d) 20 ∉ B

For ways of describing a set click here