Final answer:
When both demand and lead time are known, the key focus in inventory management shifts to determining the optimal order size to minimize associated costs and avoid stockouts.
Step-by-step explanation:
When the demand is known and the lead time is known, the single order inventory problem typically becomes a matter of Order size determination. This process involves calculating the optimum quantity of inventory to order, considering both the demand and the lead time, to minimize costs while avoiding stockouts. Companies use various inventory management models, like the Economic Order Quantity (EOQ) model, which calculates the ideal order quantity by balancing the costs associated with ordering and holding inventory.