Final answer:
The correct number of available-to-promise (ATP) items for the first period is 250 items, as it takes into account the inventory on hand, scheduled production, and subtracts the booked orders.
Step-by-step explanation:
The concept being questioned relates to inventory management, specifically the calculation of available-to-promise (ATP) which is a key component of master scheduling. To determine the ATP, you need to look at the inventory on hand, the scheduled production, and the booked orders. In the scenario provided, there are 150 units on hand and a scheduled production for 500 items. After fulfilling the booked orders of 400 items, you subtract these from the sum of inventory on hand and scheduled production (150 + 500 - 400), which leaves us with an ATP of 250 items for the first period.