Answer:
The number of units to be purchased in September are 24000 units.
Step-by-step explanation:
Based on the company's policy, the ending inventory for August or the Opening inventory for September will be 20% of September's sales.
Thus, the opening inventory is 0.2 * 20000 = 4000 units
The purchases for September should be equal to cover the Sales requirements for September along with having a closing Inventory equal to 20% of October sales.
Purchases - September = Sales requirements for September + Closing Inventory for September - Opening Inventory for September
Purchases - September = 20000 + 0.2 * 40000 - 4000
Purchases - September = 24000 units