An expression in mathematics is a statement that uses either numbers, variables, or both. For example, the following are all mathematical expressions:

y

4

6 - 4

5 × x - 7

4 + 5 (3 - 2)

x + 4 (7 - x)

In order to write an expression from a written mathematical problem, one has to interpret the text. For example, one person weighs 100 pounds and another weighs y pounds; the expression for their combined weights would be 100 + y.