In mathematics, a variable is a symbol that represents a value that can vary or change in a given context. In the expression 20 + m, the variable is represented by the symbol "m". This means that "m" can take on any value, which can be positive, negative, or zero.
To use this expression in a problem, you would need to assign a value to the variable "m". For example, if "m" represents the number of minutes spent exercising, you could assign a value of 30 to "m", which would make the expression 20 + 30. Then you would evaluate the expression by adding 20 and 30, which would give you a result of 50.
In algebra, variables are often used to represent unknown quantities, and equations can be formed by setting expressions with variables equal to each other. The value of the variable can then be found by solving the equation for the variable.