A firm’s implicit and explicit costs are explained for both short‑ and long‑run periods and total-, unit-, and marginal-cost concepts are addressed. These concepts prepare you for both ‘total-revenue, total-cost" and "marginal-revenue, marginal-cost" approaches to profit maximization. The law of diminishing returns is explained as an essential concept for understanding average and marginal cost curves. Analyze the general shape of each cost curve (AFC, AVC, ATC, MC) and the relationship they bear to one another. For example, explain the differences between the average and the marginal when a class with 40 students in it has a total weight of 6,000 pounds and a100 pound jockey joins the class versus a 350 pound sumo wrestler.