Answer:
If a store orders 100 units every time and sells 90 units each week, the average inventory can be calculated as follows:
Each time the store orders 100 units, the inventory increases by 100 units.
Each week, the store sells 90 units, so the inventory decreases by 90 units.
Assuming that the store orders new inventory as soon as it runs out, the average inventory can be estimated as the average of the minimum and maximum inventory levels.
The minimum inventory level occurs just before a new order is placed, when the inventory has been depleted to 10 units. The maximum inventory level occurs just after a new order is received, when the inventory has been replenished to 100 units.
Therefore, the average inventory is:
(10 + 100) / 2 = 55
So, the average inventory is 55 units.