4. (a) Draw the activity network described in the precedence table below, using activity on arc and the minimum number of dummies.
| Activity | Immediately preceding activities |
| A | - |
| B | - |
| C | - |
| D | A |
| E | A |
| F | A, B, C |
| G | C |
| H | E, F, G |
| I | E, F, G |
| J | H, I |
| K | H, I |
| L | D, J |
A project is modelled by the activity network drawn in (a). Each activity requires one worker. The project is to be completed in the shortest possible time. The table below gives the time, in days, to complete some of the activities.
| Activity | Duration (in days) |
| B | 7 |
| F | 4 |
| J | 4 |
| L | 6 |
The critical activities for the project are B, F, I, J and L and the length of the critical path is 30 days.
(b) Calculate the duration of activity I.
(c) Find the range of possible values for the duration of activity K .