The Ace Machine Company is considering using a priority scheduling rule in its fabrication shop and must decide whether to use: the critical rule, the order slack rule, the shortest operation next rule or the slack per operation rule.

The table below shows the companys current inventory and shop status.

Exhibit 1

Order number	Manufacturing Lead Time Remaining	Time Remaining Until Due Date	Current Operation Processing Time	Number of Operations Remaining	Total Processing Time Remaining
1	15	7	2	3	8
2	15	11	3	4	8
3	20	-2	5	2	8
4	15	-5	4	3	8
5	15	3	1	12	8

Note: Time is measured in days. Manufacturing lead time remaining includes both the machine processing time and the length of time orders spend moving and waiting to be processed in a machine queue. Current operating processing time (as well as total processing time remaining) includes no move or queue times.

a) State the formula for calculating the priority index for each of the sequencing rules given above.

b) Compute the scheduling priority index for each order in Exhibit 1 for the four sequencing rules.