6 Joan and Keith have to clear and tidy their garden. The table shows the jobs that have to be completed, their durations and their precedences.
| Jobs | Duration (mins) | Immediate predecessors |
| A | prune bushes | 100 | - |
| B | weed borders | 60 | A |
| C | cut hedges | 150 | - |
| D | hoe vegetable patch | 60 | - |
| E | mow lawns | 40 | B |
| F | edge lawns | 20 | D, E |
| G | clean up cuttings | 30 | B, C |
| H | clean tools | 10 | F, G |
- Draw an activity on arc network for these activities.
- Mark on your diagram the early time and the late time for each event. Give the minimum completion time and the critical activities.
- Each job is to be done by one person only. Joan and Keith are equally able to do all jobs. Draw a cascade chart indicating how to organise the jobs so that Joan and Keith can complete the project in the least time. Give that least time and explain why the minimum project completion time is shorter.