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. June 1 4 Units 150 400 800 1,300 300 Beginning inventory Purchase Purchase Sale Purchase Amount per Unit $30 33 36 60 39 12 16 24 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 dollars.)