One Specialist, Two Parallel Tracks
A retail chain is replacing its point-of-sale system before the November peak. The plan has these activities: A, requirements and solution design, 5 days; B, configure the reporting module, 3 days; C, build the core sales-data migration, 4 days; D, integration testing, 2 days; E, pilot in 10 stores, 6 days. B and C can start only after A and both must finish before D; E follows D. Both B and C require Priya, the only person with the data-migration skills, so they cannot run at the same time. The training team can prepare materials in 4 days once A is complete, and the materials must be ready before E starts. Payment certification by a third party takes 10 working days after D. The team has already booked a pilot launch date that assumed every activity ran at its earliest start.
1. Calculate the critical path and the total float of activity B, assuming Priya could somehow work on B and C at the same time. Show your working.
Read the worked answer
Using end-of-day numbering and A starting on day 1:
- Path A-B-D-E: 5 + 3 + 2 + 6 = 16 days.
- Path A-C-D-E: 5 + 4 + 2 + 6 = 17 days.
The critical path is A-C-D-E at 17 days. A runs days 1-5; C runs 6-9; D runs 10-11; E runs 12-17.
B's float: B can start on day 6 and would finish on day 8. D cannot start until both B and C are complete, i.e. day 10. So B's latest finish is day 9, giving total float of 1 day (9 minus 8).
The parallel training task takes 4 days from day 6, finishing day 9, and is needed before E starts on day 12, so it also has float.
The hidden issue is the payment certification: 10 working days after D gives day 21, which is later than the 17-day pilot end. That constraint, not the float, is likely to govern the real launch date and must be raised with the sponsor.
2. Given that Priya cannot work on B and C concurrently, recommend a sequence and state the effect on the earliest pilot start. Which activity should get Priya first, and why?
Read the worked answer
Resource levelling is unavoidable: the two tasks must be serialised, adding 3 days (the shorter task's duration) to the path through D, so the earliest pilot start moves from day 12 to day 15 and E finishes on day 20 instead of day 17, a 3-day slip.
Work the arithmetic both ways to show the result is the same:
- C first: C days 6-9, B days 10-12, D 13-14, E 15-20.
- B first: B days 6-8, C days 9-12, D 13-14, E 15-20.
Because the slip is identical, the decision should be made on risk, not on dates. Give Priya the core sales-data migration (C) first: it is the larger, less familiar, higher-uncertainty task, and starting it later compresses the window in which problems can be found and fixed before the November peak. Reporting configuration is more predictable and can absorb a late start. The training materials remain unconstrained either way.
The project manager should then report the 3-day slip and the certification deadline together, rather than presenting the schedule as recoverable.
3. The sponsor asks whether the pilot date can be protected by hiring a contractor for the reporting configuration. What should the project manager check before answering?
Read the worked answer
Before promising anything, the project manager should check whether the extra person actually removes the constraint:
- Is Priya the true constraint, or is it access to the POS data and tooling? If the latter, a contractor adds nothing.
- Ramp-up: recruitment lead time plus onboarding may exceed the 3 days at stake, in which case the hire protects nothing.
- Capability: can a contractor be productive on this configuration without Priya's supervision, which would consume the very capacity being created?
- Security and compliance: access to sales and payment data requires clearance, which takes time and carries risk.
- Cost versus value: the 3-day slip is only worth buying if the pilot date is a genuine hard constraint. Check the buffer to November and the cost of a later pilot (store readiness, peak-season freeze).
- Contract and knowledge transfer: who owns the work, and does the vendor's change-control clause cover it?
If ramp-up and clearance cannot be compressed, the honest answer is that the date cannot be protected and the recovery options are scope reduction or accepting a later pilot.