Running a football stadium involves innumerable predictions. For example, when stocking up on food and beverages for sale at the game, it helps to have an idea of how much will be sold. In the football stadiums in colder climates, stadium managers use expected outdoor temperature to predict sales of hot chocolate. 

a. What is the independent variable in this example? 

b. What is the dependent variable? 

c. As the value of the independent variable increases, what can we predict would happen to the value of the dependent variable? 

d. What other variables might predict this dependent variable? Name at least three.