Sample

Demand

$235$

$421$

$394$

$261$

$386$

$374$

$361$

$439$

$374$

$316$

$309$

$514$

$348$

$302$

$296$

$499$

$462$

$344$

$466$

$332$

$253$

$369$

$330$

$535$

$334$

The Doll Computer Company makes its own computers and delivers them directly to customers who order them via the Internet. Doll competes primarily on price and speed of delivery. To achieve its objective of speed, Doll makes each of its five most popular computers and transports them to warehouses across the country. The computers are stored in the warehouses from which it generally takes $1$ day to deliver a computer to the customer. This strategy requires high levels of inventory that add considerably to the cost. To lower these costs, the operations manager wants to use an inventory model. He notes that both daily demand and lead time are random variables. He concludes that demand during lead time is normally distributed, and he needs to know the mean to compute the optimum inventory level. He observes $25$ lead time periods and records the demand during each period.

a$.$ The manager would like a $90\%,95\%$ and $99\%$ confidence interval estimate of the mean demand during lead time.

b$.$ Compare and interpret the results obtained in all the $3$ scenarios.