AutoParts Ltd. uses a periodic inventory system. The following are the transactions for January.

Date	Activities	Units Acquired at Cost	Units Sold at Retail
Jan. 1	Beginning inventory	200 units @ $50 per unit
Jan. 6	Purchase	700 units @ $55 per unit
Jan. 12	Sales		600 units @ $80 per unit
Jan. 20	Purchase	500 units @ $60 per unit
Jan. 28	Sales		400 units @ $90 per unit

For specific identification, the January 12 sale consisted of 100 units from beginning inventory and 500 units from the January 6 purchase; the January 28 sale consisted of 300 units from the January 20 purchase and 100 units from the January 6 purchase.

Required:

1. Calculate the COGS and ending inventory using FIFO and LIFO methods.
2. Determine the gross profit using the weighted average cost method.
3. Analyze the impact of inventory costing methods on AutoParts Ltd.'s cash flow.
4. Discuss how the choice of inventory costing method can influence managerial decision-making.