. Here’s one way to look at the inputs and outputs of a function. Think of the domain as a group of people and the range as several places. Can a person be in more than one place at a time? Of course not! You can’t be at the mall and your house at the same time. Since people represent the domain, this scenario shows that you cannot have a domain value assigned to more than one range value. Remember, in order for a relation to be a function, each value in the domain must be assigned to exactly one value in the range. But can more than one person be at the same place at the same time? Sure . This happens all the time. When you are at the mall, many other people are shopping there too. When you are at school, so are your classmates! Since place represents the range, this scenario shows that you can have more than one domain value, people, assigned to the same range value, place. We only need to be sure that in a function each value in the domain is assigned to exactly one value in the range.