Explain how the perpetual and periodic inventory systems differ, especially in determining Cost of Goods Sold and Ending Inventory? Once a retailer has chosen the inventory system they then have a choice of inventory costing methods: First-In-First-Out (FIFO), Last-In-First-Out (LIFO), weighted average and specific identification. In times of changing inventory prices (both inflation and deflation) how can the choice of the inventory costing method impact reported profits?