102,3 Periodic Inventory System and Inventory Costing Methods E4A. In chronological order, the inventory, purchases, and sales of a single product for a recent month are as follows. 1. Using the periodic imventory system, compute the eost of ending inventory, cost of goods sold, and gross margin. Use the average-cost, HHO, and LIFO inventory costing methods. (Round unit costs to cents and totals to dollars.) 2. ACCOUNTING CONNECTION - Explain the differences in gross margin produced by the three methods