Question no. 6.8 it was told that the demand for a product is 12,500 units for a three month period. Each unit of product has a purchase price of $15 and ordering costs are $20 per order placed. The annual holding cost is 10% of its purchase price. Why is the answer like this : D = 12,500 × 4 = 50,000 instead of D = 12,500 × 3 = 37,500 ?