Helix Corporation uses the weighted-average method in its process costing system. It produces prefabricated flooring in a series of steps carried out in production departments. All of the material that is used in the first production department is added at the beginning of processing in that department. Data for May for the first production department follow: Units Percent Complete Materials Conversion Work in process inventory, May 1 66,000 100% 50% Work in process inventory, May 31 46,000 100% 30% M