The cafeteria of a certain elementary school provides a free lunch every day to the entire student body — a significant expense in the school's annual budget. A vice principal was exploring cost-reducing measures that would not compromise nourishment. A local Italian restaurant offered the school a large number of pizzas at a vastly reduced bulk rate. The pizzas were served one day, and afterward, the vice principal calculated that the cost of the pizza and delivery was slightly more than the average cost of typical cafeteria lunch day. Therefore, he concluded that the school could not save money by replacing a day of cafeteria lunch with a day of pizza from this restaurant.
Which of the following would be most useful for evaluating the conclusion drawn by the vice principal?