In an actual (historical) cost system that uses process costing, the presence of partially completed inventory a the end of an accounting period results in a second accounting problem: the treatment of the cost of that inventory in the next accounting period. The solution is to select a cost flow assumption like those used in accounting for non-manufacturing inventories. In practice the most common cost flow assumption for process costing is the weighted-average cost method, which averages or blends the costs of the incomplete beginning inventory with all the costs incurred in the current period this method is discussed in detail in Chapter 6. Professional certification examinations for accountants also require familiarity with the first-in. first-out cost flow assumption. which is discussed in Chapter 6.