A variable is a symbol used to represent a number. In the expression 8x + 17, x is the variable. In the equation = 25, y is the variable. Variables need not be letters; for example, the expression 6 + 2 contains the variable .
An expression or equation may contain more than one variable. The expression 7 - 3r + 12t contains the variables r and t, and the equation 6y = 24x contains the variables x and y.
An algebraic expression is an expression that contains one or more variables.
An algebraic equation is an equation that contains one or more variables.
Note: When we write two quantities next to each other, or next to each other separated by parenthesis, the multiplication sign is implied. For example, 4r means 4×r and 3(4 + 2) means 3×(4 + 2).
We can represent word statements by algebraic expressions and equations. For example, "the number of apples in the bucket plus 5 more apples" can be represented by the expression a + 5. The statement "twice the number of miles I ran is equal to 12" can be represented by the equation 2m = 12. Here are the steps to writing a word statement as an expression or an equation: