Inventory management - Multiple replenishment opportunities (2)

A supplier for an electronics store has introduced quantity discounts to encourage larger order quantities of cameras. The price schedule is:

Quantity purchased	Price per unit
fewer than 525	$80
at least 525	$75

Suppose the monthly demand at a retail store that buys from this retailer and resells is 175 units. The supplier charges a fixed cost of $180 per shipment. The cameras are expected to sell well for multiple seasons, so multiple replenishment opportunities are possible.

The retailer implements continuous review to manage inventory. What is the stock-out probability the retailer achieves by setting the reorder point to 800 units if the standard deviation of the monthly demand is 20 and the supplier can guarantee a 4-month lead time?