Independent variable

We already know that "independent variable" is another way of saying "domain", "x", or "input". However, we need to be able to look at a situation and determine which variable is independent of everything else.

Example 1: Let's say your cell phone plan charges you for every text message you send. Obviously, the more text messages you send, the more your monthly bill will be. In this scenario, there are two important variables: 1) how many text messages you send, and 2) your total monthly bill.

To determine which one is the independent variable, think about which one you directly control. You can only control how many text messages you send. Therefore, the number of text messages you send is the independent variable.