. Deriving the short-run supply curve Consider the competitive market for halogen lamps. The following graph shows the marginal cost (MC), average total cost (ATC), and average variable cost (AVC) curves for a typical firm in the industry. 100 T 90 80 70 60 ATC 50 A 40 30 AVC 20 MCO 10 10 20 30 40 50 60 70 80 90 100 QUANTITY (Thousands of lamps)