A family is preparing to go to a footy game. Their house has two showers. Mother insists that the entire family eats together at breakfast time. Their morning preparations are shown below...
| Number | Task | Duration (min) | Person | Depends on |
|---|---|---|---|---|
| 1 | alarm goes off | 5 | father | none |
| 2 | wake family | 5 | father | 1 |
| 3 | mum shower | 40 | mother | 2 |
| 4 | son shower | 30 | son | 2 |
| 5 | walk dog | 10 | father | 2 |
| 6 | father shower | 15 | father | 5 |
| 7 | prepare breakfast | 15 | mother | 3 |
| 8 | eat breakfast | 15 | all | 7 |
| 9 | load car | 5 | all | 8 |
| 10 | drive to game | 25 | all | 9 |
- In the PERT example below, notice the dummy tasks leading from tasks 4 and 6 to task 8. They indicate that task 8 (eating breakfast) cannot proceed until tasks 4 (son's shower/dress) and 6 (father shower/dress) are completed. Of course, task 8 also cannot proceed until its predecessor, task 7 (prepare breakfast) is complete.
- To make things a little clearer why the lines appear as dummy tasks... after tasks 4 and 6, a dependency must be shown leading to task 8. But drawing a normal task arrow from tasks 4 and 6 to task 8 implies that something needs to be done on those arrows, but there is no task, just the dependency. That's what the dummy (dotted) task shows... a dependency that exists even when there is no task between two tasks.
Bonus questions: (to see the answers, use your mouse to highlight the invisible text between >> and << )
Q1. What is the critical path?
ANSWER IS IN HERE >> Alarm, Wake All, Mum Shower, Prep Brekky, Eat, Load car, Drive <<
Q2. What is the minimum time it would take for the family to reach the footy game after getting the alarm goes off?
ANSWER IS IN HERE >>The total of the critical task durations : 5 + 5 + 40 + 15 + 15 + 5 + 25 = 110 minutes<<
Q3. How much more time could dad walk the dog before eating breakfast got delayed?
ANSWER IS IN HERE >> 30 minutes <<
Q4. What is this amount of time called?
ANSWER IS IN HERE >> Slack time <<
Q5. If mum skipped her 40 minutes shower, how much earlier would they get to the game?
ANSWER IS IN HERE >> 25 minutes <<
Q6. Redraw the PERT chart as a Gantt chart.
Q7. Redraw the PERT chart to show how events would change if the family had only one shower rather than two. How would their arrival time at the game be affected?
Credits
The neat example above was adapted from http://www.tks.buffalo.edu/~scomings/Sgc/proj.html by Stephen G. Comings, based on a lecture by John Storck at the University of Buffalo, USA, 1998