A symbol which has a fixed numerical value is called a constant. For example: 2, 5, 0, -3, -7, 2/7, 7/9 etc., are constants. NUMBER of days in a week represents a constant. In the expression 5X + 7, the constant term is 7. Variables: A quantity which has no fixed value but takes no various numerical values is called a variable.  For example: TEMPERATURE at different times of a day represents a variable. 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. Examples on Constants and Variables: (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.Step-by-step explanation: