This is the number of elements in a set. It is written by the symbol n(A), n(A) means cardinal number of the set A.

Types of sets

1. Universal set:

This is a set that contains all the other sets. It is represented by the symbol U or Є. Example:

Є= (x:x all the students in form1)

U= (x:x all the people living in bepanda)

2. Complement of a set:

The complement of a set is the set of element not found in a set but found in the universal set. The complement of a set is represented

either by a small apostrophe (A‘) or a small letter (A_c or A^c) on the set of letters. Example:

Given that Є= (1, 2, 3, 4, 5, 6) and B= (2, 4, 6), find B’ or B_c

Solution: B’= (1, 3, 5)

3. Finite set:

A set is said to be finite if it has an end or a limit. Example;

A= (1, 2, 3, 4, 5), while an infinite set: is said to be infinite because it has no end or limit. Example; A= (1, 2, 3, 4, 5-----)

4. Equivalent set:

Two or more sets are equivalent if they both have the same cardinal number. Example:

Given the sets A= (1, 2, 3, 4) and B= (a, b, c, d), then the set A is equivalent to B since; n(A)= n(B)= 4

We use the symbol ≡ to represent equivalence. That is A≡B

5. Unit set:

A unit set is one with only one element or a cardinal number. For example; A= (9), B= (6)

All of the above are unit sets with cardinal number 1.

6. Sets of numbers:

N= (natural numbers= 1, 2, 3, 4, ----)

Z= (integers= ---- -3, -2, -1, 0, 1, 2, 3, ----)

Q= (rational numbers= ½, 2/3, ¾, ----)

R= (real numbers= 0, 1, 2, 3------)