Periodic Inventory by Three Methods; Cost of Merchandise Sold The units of an item available for sale during the year were as follows: Jan. 1 Inventory 50 units @ $118 Mar. 10 Purchase 40 units @ $128 Aug. 30 Purchase 20 units @ $132 Dec. 12 Purchase 90 units @ $136 There are 80 units of the item in the physical inventory at December 31. The periodic inventory system is used.