Constants and Variables are the two types of symbols in algebra.



Constant:

A symbol which has a fixed numerical value is called a constant,
e.g., 2, 5, 0, -3, -7, 2/7, 7/9 etc., are constants.

Variables:

A quantity which has no fixed value but takes no various numerical values is called a variable.



For example:

The height of a student in your grade is a variable, as it varies from student to student. A variable is denoted by a letter like x, y, z, u, v etc.
A combination of a constant and a variable is also a variable.



For example:

(i) In 2a, 2 is a constant and a is a variable.

(ii) In -7mn, -7 is a constant and m and n are variables.

(iii) In 3x, 3 is constant and x is variable but together 3x is a variable.

(iv) If 3 is a constant and x is a variable, then 3+x, 3-x, 3/x, 3x, x/3, etc., are also variables.

So, we conclude that the combination of a constant and a variable is always a variable.