What is the difference between a weighted-average method of process costing and a first-in, ...

The weighted average method computes unit costs by dividing total costs entering the
work-in-process account (whether from beginning work-in-process or from work started during the period) by total equivalent units completed to date, and assigns this average cost to units completed and to units in ending work-in process inventory.

The first-in, first-out (FIFO) method computes unit costs based on costs incurred during the current period and equivalent units of work done in the current period. It assigns the costs of beginning work-in-process inventory to the first units completed, and it assigns costs of the equivalent units worked on during the current period first to complete beginning inventory, next to start and complete new units, and finally to units in ending work-in-process inventory.