4.21 FIFO method. (20 min) 1 The equivalent units of work done in the Assembly Department in October 2010 for direct materials and conversion costs are the same as in problem 4.20 and are shown in Solution Exhibit Ab The cost per equivalent unit of work done in the Assembly Department in October 2010 for direct materials and conversion costs are calculated in problem 4.20 in Solution Exhibit B. 3 Solution Exhibit 4.21 summarises the total Assembly Department costs for October 2010, and assigns these costs to units completed (and transferred out) and units in closing work in progress under the FIFO method. The cost per equivalent unit of opening stock and of work done in the current period differ