Periodic Inventory by Three Methods Dymac Appliances uses the periodic inventory system. Detalis regarding the inventory of appliances at January 1 , purchases invoices during the next 12 months, and the inventory count at December 31 are summarized as follows: Kequired: 1. Determine the cost of the inyentory on December 31 by the firatin, first-ach method. If the irveotory of a particular model comprtses one entire purchase plus a portion of another purchase acquired at a different urit cost, uge a separate line for each purchase. If units are in inventory at two different costs. enter the unit5 PGiRCHASED MOST RECENTLY first. If the inventery of a particular model comprises one entire purchase plus a portion of another purchase-acquired at a different unit cost, use a separate line for each purchase. If units are in inventory at two different costs, enter the OLDEST units first. 2. Determine the cost of the inventory on December 31 by the lastin, first-out method. If the inventory of a particular model comprises one entire purchase plus a portion of another purchase acquired at a different unit cost. use a separate 3. Determine the cost of the inventory on December 31 by the weighted average cost method. 4. would be preferred for income tax purposes in periods of rising prices