A variable is a symbol that represents a number. Usually we use letters such as n, t, or x for variables.
For example, we might
say that s stands for the side-length of a square. We now treat s as if it were a number we could use. The perimeter of the
square is given by 4 × s. The area of the square is given by s × s
When working with variables, it can be helpful to use a letter
that will remind you of what the variable stands for: let n be the number of people in a movie theater; let t be the time it takes to
travel somewhere; let d be the distance from my house to the park.
Equations.
An equation is a statement that two numbers or expressions are equal.
