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2/28: More CPM: Crashing

2/28: More CPM: Crashing. Roll call / return exams / return homework Review: Critical Path Management Creating the CPM diagram Calculating the critical path Calculating the ES & EF, the LS & LF Calculating the slack

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2/28: More CPM: Crashing

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  1. 2/28: More CPM: Crashing • Roll call / return exams / return homework • Review: Critical Path Management • Creating the CPM diagram • Calculating the critical path • Calculating the ES & EF, the LS & LF • Calculating the slack • Crashing: When you’re willing to spend money to get the project done sooner. • Small Group Exercise • Homework for the week

  2. Exam Scores • Maximum: 100% (four people) • Minimum: 63% • Mean & Median: 88% • Correct exams are available at:http://www.adbook.net/teach022/305/m.htm

  3. D 4 F 5 A 4 C 2 start finish E 7 B 5 G 1 CPM: Creating the Diagram

  4. D 4 F 5 A 4 C 2 start finish E 7 B 5 G 1 CPM: Calculating the Critical Path Possible paths from start to finish: A-C-D-F A-C-E B-G 4+2+4+5 = 15 4+2+7 = 13 5+1 = 6

  5. CPM: Calculating the ES & EF Early start: how soon it can start Early finish: ES + Duration D | 6 10 4 | F | 10 15 5 | A | 0 4 4 | C | 4 6 2 | start finish E | 6 13 7 | B | 0 5 5 | G | 5 6 1 |

  6. CPM: Calculating the LS & LF Late finish: the last possible time it must be done to not affect the overall project time. Late start: LF - Duration D | 6 10 4 | 6 10 F | 10 15 5 | 10 15 A | 0 4 4 | 0 4 C | 4 6 2 | 4 6 start finish E | 6 13 7 | 8 15 B | 0 5 5 | 9 14 G | 5 6 1 | 14 15

  7. CPM: Calculating the slack Slack: how much “wiggle room” you have for an activity Slack = LS – ES = LF - EF S=0 S=0 D | 6 10 4 | 6 10 S=0 S=0 F | 10 15 5 | 10 15 A | 0 4 4 | 0 4 C | 4 6 2 | 4 6 start finish S=2 E | 6 13 7 | 8 15 S=9 S=9 B | 0 5 5 | 9 14 G | 5 6 1 | 14 15

  8. Crashing: Buying Time • Sometimes you can buy a quicker time for an activity • Paying overtime • Paying for another worker to help • Paying for guaranteed quicker delivery (EX: FedEx) • But is it worth it?

  9. Crashing Activity Times • Things to consider: • Is the activity on the critical path? • How much will it cost to crash the activity? • Are there other activities that are more cost-effective to crash? • How much do you need to crash the project time?

  10. Crashing Activity Times: Example Shorten project by 2 days while minimizing costs.

  11. Crashing Activity Times: Example Shorten project by 2 days while minimizing costs. First, calculate the cost/day to crash each activity.

  12. Crashing Activity Times: Example Shorten project by 2 days while minimizing costs. Next, see what’s on the critical path.

  13. Crashing Activity Times: Example Shorten project by 2 days while minimizing costs. Finally, see what the cheapest way to reduce is.

  14. D 4 F 5 A 4 C 2 start finish E 7 B 5 G 1 Crashing Activities: Watch Out • If we had to crash the project by more than two days, we would have had to look again – the critical path may change. A-C-D-F A-C-E B-G 4+2+4+5 = 15 4+2+7 = 13 5+1 = 6

  15. Small Group Exercise Crash the project by 3 days while minimizing costs.

  16. Homework: Do it on PAPER • Ch. 10 #21 a & b • Ch. 10 #22 b & c • Ch. 10 #24 a, c, d (use 26 weeks), & f

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