The following jobs are waiting to be processed at Keah-Lan’s machine center.
Job Date Order Received Processing Days Needed Date Order Due, End of Day __
A 110 20 180
B 120 30 200
C 122 10 175
D 125 16 230
E 130 18 210
The jobs are listed in the order in which they were received. Suppose that it is now the start of day 151, so day 151 is a work day on the planning calendar and none of the above jobs have been started yet. There are no other jobs waiting or in the system at this time. All the resources required for each job are on hand. Once a job is started, it will not be stopped until it is completed. Each job is scheduled to be worked on the machine center’s only machine.
a) In what sequence should the jobs be ranked according to the following rules?
• CR: Ratio of remaining time until the job is due/remaining processing time
• EDD: Earliest due date
• LPT: Longest processing time
b) For the CR and LPT, what is the sequence of these two rules based on each of the following criterion?
• Average flow time measured from now (start of day 151)
• Average lateness with no credit for being early
• Average days early with no penalty for being late
