Question
Parts P1-P7 are machined first on a milling machine and then polished at a separate machine. Using the information in the following table, the minimum total completion time required for carrying out both the operations for all 7 parts is __________ hours.
| Part | Milling (hours) | Polishing (hours) |
| P1 | 8 | 6 |
| P2 | 3 | 2 |
| P3 | 3 | 4 |
| P4 | 4 | 6 |
| P5 | 5 | 7 |
| P6 | 6 | 4 |
| P7 | 2 | 1 |
Options :
31
33
30
32
Answer :
33
Solution :
According to Johnson's algorithm, optimum job sequence is,
P3 → P4 → P5 → P1 → P6 → P2 → P7
| Part | Miling ( hours) | Polishing (hours) | ||||
| In time | Processing time |
Out time | In time |
Processing time |
Out time |
|
| P3 | 0 | 3 | 3 | 3 | 4 | 7 |
| P4 | 3 | 4 | 7 | 7 | 6 | 13 |
| P5 | 7 | 5 | 12 | 13 | 7 | 20 |
| P1 | 12 | 8 | 20 | 20 | 6 | 26 |
| P6 | 20 | 6 | 26 | 26 | 4 | 30 |
| P2 | 26 | 3 | 29 | 30 | 2 | 32 |
| P7 | 29 | 2 | 31 | 32 | 1 | 33 |
The minimum total completion time required for carrying out both the operations for all 7 parts is 33 hours.
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