Project Management: Scope, Schedule, and the Critical Path
The four constraints
Projects are bounded by scope, time, cost and quality; moving one moves the others. Decompose deliverables with a work breakdown structure into work packages, then estimate durations and sequence activities into a network. The critical path is the longest chain of dependent activities through that network. It determines the shortest possible project duration and carries zero total float. Activities off the path have float and can slip without moving the end date, until that float is consumed.
Traps to expect
Exam items often label the most important or highest-risk activity as "critical path." That is wrong; criticality is a scheduling property, not a priority judgement. Equally common: confusing a milestone (a zero-duration checkpoint) with a task, or assuming that crashing always shortens the schedule. Adding resources to a non-critical path buys nothing. A RACI chart should show exactly one Accountable person per task, with several Responsible and the necessary Consulted and Informed; two A's is a defect. Change control, meaning log the request, assess impact, approve or reject, and rebaseline, is what protects the plan from scope creep.
Rule of thumb
Float equals how much an activity can slip before it joins the critical path.
Worked example
Activity A takes 5 days. B follows A and takes 4 days; C follows A and takes 9 days. D follows both B and C and takes 2 days. Path A-B-D is 11 days; A-C-D is 16 days. The critical path is 16 days, and B has 5 days of float.