operations research

1. Retailers plan to purchase certain items for the next five months. Retailer needs each month are given in the table below: Retailers place orders at the beginning of each month. At the beginning of January the retailer had no inventory of these items. Any remaining units at the end of a month will be used in the following month at a cost of IDR 20 /unit. The cost of each order is IDR 300 . The retailer can only order in lot sizes of 10,20 , or 30 units and the maximum quantity he can order each month is 60 units. Warehouse storage capacity is 40 units maximum, if there are more than 40 units left at the end of the month, the units are discarded at a cost of Rp.100 How many units should retailers order each month