Mathematical expressions or phrases may contain variables. Variables are symbols used to represent numbers. Values of the number can change depending on other numbers and variables in the expression. Expressions may be numerical or algebraic. Numerical expressions contain only numbers. An example of such an expression is 9 + 8, and is represented by a single number, 17. Algebraic expressions consist of numbers and variables. An example of an algebraic expression is 9 + x.

When working with math expressions, it is sometimes necessary to simplify the expression. This involves combining similar terms and removing parenthesis by using the distributive property. There are four basic steps involved when solving mathematical problems involving expressions. To do this, group terms carrying the same variable in the math expression, and then simplify the variable by doing the mathematical operations in brackets. Perform multiplication and division operations, starting from left to right. Finally, perform the addition and subtraction operations starting from left to right.