# Comprehension Four jobs are to be processed on a machine as per data listed in the table. Job Processing time (in days) Due date 1 4 6 2 7 9 3 2 19 4

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### Comprehension

Four jobs are to be processed on a machine as per data listed in the table.

 Job Processing time (in days) Due date 1 4 6 2 7 9 3 2 19 4 8 17

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Correct Answer - Option 4 : 8

Answer: 4

Concept:

Shortest Processing Time (SPT): Sequence of the job is based on ascending order of processing time.

Processing time: The time spent by a job on machine.

Due date: Expected completion time of a job.

Flow time: Time spend by a job on shop floor. Cumulative addition of Processing time.

Make span: Time interval between starting of 1st job & coming out of last job in all machine.

Earliness/Tardiness: Time difference between Flow time and Due date time.

• Earliness: When time difference is negative i.e. Job comes out before due date.
• Put ‘0’ under tardiness.
• Tardiness: When time difference is positive i.e. Job comes out after due date.
• Put ‘0’ under earliness.

Calculation:

 Job Processing Time Flow Time Due date Tardiness 3 2 2 19 0 1 4 6 6 0 2 7 13 9 4 4 8 21 17 4

∴ Total tardiness = 4 + 4 = 8.

Important Points:

 Method Definition First Come First Serve (FCFS) Jobs are arranged as per they arrived Shortest Processing Time (SPT) Jobs are arranged as per the ascending order of Processing Time. Earliest Due Date (EDD) Jobs are arranged as per the ascending order of Due date. Critical Ratio (CR) $C.R = \frac{{Due\;date}}{{Procesisng\;Time}}$ Jobs are arranged as per the ascending order of Critical Ratio.

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