5 The activity network and table together show the tasks involved in constructing a house extension, their durations and precedences.
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| Activity | Description | Duration (days) |
| A | Architect produces plans | 10 |
| Pl | Obtain planning permission | 14 |
| Demo | Demolish existing structure | 3 |
| Fo | Excavate foundations | 4 |
| W | Build walls | 3 |
| Pb | Install plumbing | 2 |
| R | Construct roof | 3 |
| Fl | Lay floor | 2 |
| E | Fit electrics | 2 |
| WD | Install windows and doors | 1 |
| Deco | Decorate | 5 |
- Show the immediate predecessors for each activity.
- Perform a forward pass and a backward pass to find the early time and the late time for each event.
- Give the critical activities, the project duration, and the total float for each activity.
- The activity network includes one dummy activity. Explain why this dummy activity is needed.
Whilst the foundations are being dug the customer negotiates the installation of a decorative corbel. This will take one day. It must be done after the walls have been built, and before the roof is constructed. The windows and doors cannot be installed until it is completed. It will not have any effect on the construction of the floor.
- Redraw the activity network incorporating this extra activity.
- Find the revised critical activities and the revised project duration.