The basic operations of decimal numbers consist of addition, subtraction, multiplication, and division. By the end of fifth grade it is expected that students are able to perform these operations with positive and negative decimal numbers.

An inverse operation is an action put forth on an expression as opposed to an inverse, which is a particular value or expression. For example, the inverse operation of addition is subtraction whereas the additive inverse of 2 is (-2).

Inverse operations are used when solving a problem for a particular variable in Algebra 1. Consider the equation ax = 5 where a is a constant and x is a variable. In order to solve for x, one must recognize that x is being multiplied by a. Therefore, to isolate the x, the inverse operation of multiplication (i.e., division) is applied to the equation. Thus,

Division is the operation which isolates x. 

Consider thinking about inverse operations as this: If a value is being acted upon by an operation, the inverse operation returns back the original value.