FIT5057 · Project Management
Schedule and Cost Management
This is the most calculation-heavy chapter. It turns the WBS into a schedule and a budget. You sequence activities with the precedence diagramming method (PDM) and its four dependency types (FS, SS, FF, SF), estimate durations with PERT (the three-point weighted average), and find the schedule with the Critical Path Method (CPM) — a forward pass for earliest dates, a backward pass for latest dates, and float = latest − earliest. The critical path is the longest, zero-float chain; it sets the deadline. A worked six-activity network shows every cell. The chapter then covers the Gantt chart and cost planning: estimate types and accuracy ranges, and the two kinds of reserve (contingency for known risks, management for unknown). These calculations are light in the quiz (which tests recognition) but central to the predictive project assignment.
What this chapter covers
- 015.1 From scope to schedule — the six-step process
- 025.2 PDM & the four dependency types (FS, SS, FF, SF)
- 035.3 Network notation (AON vs AOA)
- 045.4 PERT — the three-point estimate
- 05The Critical Path Method — forward pass, backward pass, float
- 06Worked CPM — a six-activity network
- 075.5 The Gantt chart
- 085.6–5.7 Cost estimate types & the two kinds of reserve
Worked example: a PERT three-point estimate
- +1Recall the PERT formula: expected time tE = (optimistic + 4 × most likely + pessimistic) ÷ 6 — a weighted average that gives the most likely value four times the weight.
- +1Substitute: tE = (4 + 4×6 + 14) ÷ 6 = (4 + 24 + 14) ÷ 6 = 42 ÷ 6.
- +1Compute and interpret: tE = 7 days. It exceeds the most likely 6 days because the long pessimistic tail (14) pulls the weighted average up — PERT accounts for skew that a single point estimate ignores.
Key terms
- Finish-to-start (FS) dependency
- The most common precedence relationship: the predecessor must finish before the successor can start (you must dig the trench before you lay the pipe). The other three PDM types are start-to-start (SS), finish-to-finish (FF) and start-to-finish (SF).
- PERT (three-point estimate)
- Program Evaluation and Review Technique: the expected duration tE = (optimistic + 4×most-likely + pessimistic) / 6, a weighted average that handles uncertainty and skew better than a single point estimate by weighting the most likely value four times.
- Critical path
- The longest path of dependent activities through the network, and therefore the shortest possible project duration. Its activities have zero float; any slip on the critical path slips the whole project. It is found with the Critical Path Method (forward and backward passes).
- Float (slack)
- How long an activity can be delayed without affecting something else. Total float = latest start − earliest start (delay without slipping the project); free float = delay without slipping any successor. Critical-path activities have zero float; float is never negative in a feasible plan.
- Contingency vs management reserve
- Two kinds of buffer. Contingency reserve covers known risks (identified, in the cost baseline, controlled by the PM). Management reserve covers unknown risks (unforeseen work, outside the baseline, released by management). Confusing the two is a quiz trap.
Schedule and Cost Management FAQ
Why is the critical path the longest path, not the shortest?
Because the project cannot finish until every path is complete, and the longest path takes the most time — so it sets the minimum project duration. It is called "critical" precisely because it has zero float: any delay on it delays the whole project. A common wrong answer calls it the shortest path; it is the opposite.
How do I tell finish-to-start from start-to-start?
Ask what must happen to the predecessor before the successor moves. Finish-to-start (FS): the predecessor must finish first (lay the foundation, then build the walls). Start-to-start (SS): the predecessor only needs to start (begin pouring concrete, then start levelling it shortly after). FS is by far the most common; SS lets work overlap.
What is the difference between total float and free float?
Total float is how long an activity can slip without delaying the project finish; free float is how long it can slip without delaying any successor's earliest start. Free float is always less than or equal to total float. In the worked network, B has 3 days of total float but 0 free float, because using it eats E's slack — the float is shared along the path.
Is the maths heavy in the quiz?
No. The Quiz/Test rewards recognition: which dependency type is this, which activity has zero float, what does a negative variance mean. Full multi-step CPM, PERT and EVM calculations matter most for the predictive project assignment, where you have time and tools (ProjectLibre). Learn the calculations to apply them; learn the one-line interpretations for the quiz.
Exam move
Drill the CPM passes until they are mechanical: forward pass for earliest dates (take the max where activities merge), backward pass for latest dates (take the min where they split), then float = latest − earliest, and read the zero-float chain as the critical path. Memorise the PERT formula and the FS/SS/FF/SF definitions for fast quiz recognition. Keep the two reserves straight (contingency = known, in baseline; management = unknown, outside baseline) and the estimate accuracy ranges (rough order of magnitude is wide and early; definitive is narrow and late). For A1, this chapter is the scheduling and costing engine — build the network carefully because every later artefact depends on it.
