**Functions** are rules that link **inputs** and **outputs**.

In a function, each input has **only one corresponding value** as an output.

**Here is an example of a function with a rule times by 2:**

However, the picture below does **not** show a function, just a relationship between numbers:

This is because 1 is linked with two outputs, and in functions, each input must have **only one corresponding output**.

In this activity, we will identify functions accurately and use function relationships to find missing inputs or outputs.