etermine the costs assigned to ending inventory when costs are assigned based on the weighted average method. lote: Round your per unit costs to 2 decimal places. Trey Monson starts a merchardising business on December 1 and enters into the following three inventory purchases. Monson uses a perpetual inventory system. Also, on December 15, Monson sells 15 units for $20 each. Purchases on Decenter ? Purebases on Decerber 14 Furchases on Decenbes 21 10 unitg is 5 cost 20 units 512 cost 25 unita $14 cost