Periodic Inventory by Three Methods The units of an item available for sale during the year were as follows: There are 1,500 units of the item in the physical inventory at December 31 . The periodic inventory system is used. a. Determine the inventory cost by the first-in, first-out method. b. Determine the inventory cost by the last-in, first-out method. c. Determine the inventory cost by the weighted average cost method