Diminishing marginal product means that the marginal product of an input declines as the quantity of the input increases. 4. Figure 4 shows a production function that exhibits diminishing marginal product of labor.
Figure 5 shows the associated total-cost curve. The production function is concave because of diminishing marginal product, while the total-cost curve is convex for the same reason. 236 Chapter 13/The Costs of Production
Figure 4 Figure 5
5. Total cost consists of the costs of all inputs needed to produce a given quantity of output. It includes fixed costs and variable costs. Average total cost is the cost of a typical unit of output and is equal to total cost divided by the quantity produced. Marginal cost is the cost of producing an additional unit of output and is equal to the change in total cost divided by the change in quantity. An additional relation between average total cost and marginal cost is that whenever marginal cost is less than average total cost, average total cost is declining; whenever marginal cost is greater than average total cost, average total cost is rising.
Figure 6 6. Figure 6 shows the marginal-cost curve and the average-total-cost curve for a typical firm. It has three main features: (1) marginal cost is rising; (2) average total cost is U-shaped; and
(3) whenever marginal cost is less than average total cost, average total cost is declining; whenever marginal cost is greater than average total cost, average total cost is rising.
Marginal cost is rising for output greater than a certain quantity because of diminishing returns. The