Periodic Inventory System and Inventory Costing Methods E4B. In chronological order, the inventory, purchases, and sales of a single product for a recent month are as follows. June 1 Beginning inventory 4 Purchase 12 Purchase 16 Sale 24 Purchase Units Amount per Unit 150 $ 60 400 800 1,300 120 300 78 66 72 1. Using the periodic inventory system, compute the cost of ending inventory, cost of goods sold, and gross margin. Use the average-cost, FIFO, and LIFO inventory costing methods. (Round unit costs to cents and totals to dollar.) 2. ACCOUNTING CONNECTION Explain the differences in gross margin produced by the three methods