. To facilitate the project planning, the EE managers have broken the project into specific tasks. These tasks, along with their immediate predecessors and estimated duration times for fast and slow workers, respectively, are indicated in the following table.
| Task | Predecessor | Fast Time
(Days) |
Slow Time
(Days) |
| A. Check electrical panels and circuits | NA | 1.5 | 3 |
| B. Replace all light bulbs | NA | 4 | 7 |
| C. Clean and service compressor in
air conditioner |
A | 2 | 4 |
| D. Test and service heater | A | 3 | 5 |
| E. Refill oil tanks | NA | 0.5 | 5 |
| F. Clean and service electro-static filter | C, D | 1 | 3 |
| G. Clean and service blower unit | C, D | 2 | 4 |
For each task, EE directors can hire one of two possible contractors to perform the task. For each task, a less expensive contractor can be hired who charges $20 per day but works at the slow rate, or a more expensive contractor can be hired at $50 per day who works at the fast rate. Because tasks A and B both require the services of an electrical contractor, EE directors have required that the same contractor perform both tasks A and B. Also, the cost of filling the oil tanks is not a function of the time required; the cost is strictly a function of the number of gallons of oil needed (estimated currently at 15,000 gallons @ $1.75/gallon). EE Bank has employed you to handle the project; they have stated that they want the project completed at the lowest possible cost, but that the project must be completed within 9 days in order to minimize disruption. Determine which contractors should be hired; what is the estimated total cost for the overhaul? When should each contractor begin work?
