CST CPM & PERT Schedule Development 2 — Questions and Answers
Question 1: In PERT analysis, the Beta distribution is used because it:
- Assumes symmetrical uncertainty around the most likely estimate
- Can model skewed distributions with defined minimum and maximum bounds (Correct answer)
- Requires only two time estimates instead of three
- Produces the same result as a triangular distribution
Correct answer: Can model skewed distributions with defined minimum and maximum bounds
The Beta distribution is favored in PERT because it accommodates skewness and is bounded by the optimistic and pessimistic estimates.
Question 2: A project network has activities A→C, A→D, B→D, C→E, D→E. Which activities constitute the longest path if durations are A=3, B=2, C=4, D=1, E=5?
- A→C→E with duration 12 (Correct answer)
- A→D→E with duration 9
- B→D→E with duration 8
- A→C→E with duration 12 and A→D→E with duration 9 are tied
Correct answer: A→C→E with duration 12
Path A→C→E = 3+4+5 = 12, which is longer than A→D→E (3+1+5=9) and B→D→E (2+1+5=8).
Question 3: When performing a forward pass in CPM, the Early Start of a successor activity with multiple predecessors is determined by:
- The minimum Early Finish among all predecessors
- The maximum Early Finish among all predecessors (Correct answer)
- The average Early Finish of all predecessors
- The Early Finish of the predecessor on the critical path
Correct answer: The maximum Early Finish among all predecessors
An activity cannot start until all predecessors are complete, so its Early Start equals the maximum Early Finish of all predecessors.
Question 4: In a Precedence Diagramming Method (PDM) network, a Finish-to-Start relationship with a lag of 5 days means:
- The successor starts 5 days before the predecessor finishes
- The successor starts at least 5 days after the predecessor finishes (Correct answer)
- The successor finishes 5 days after the predecessor finishes
- The predecessor must finish within 5 days of the successor starting
Correct answer: The successor starts at least 5 days after the predecessor finishes
A positive lag on an FS relationship delays the successor's start by the lag duration after the predecessor finishes.
Question 5: Which of the following best describes 'free float' in CPM scheduling?
- The amount of time an activity can be delayed without delaying any successor's Early Start (Correct answer)
- The total amount of time an activity can be delayed without delaying the project end date
- Float shared between two or more activities on the same path
- The difference between an activity's Late Finish and Early Finish
Correct answer: The amount of time an activity can be delayed without delaying any successor's Early Start
Free float is the delay an activity can absorb without pushing out the Early Start of any of its immediate successors.
Question 6: A scheduler uses PERT and calculates the standard deviation of the critical path as 3 days. What is the probability the project finishes within the expected duration?
- 100%
- 84.1%
- 50% (Correct answer)
- 68.3%
Correct answer: 50%
The PERT expected duration corresponds to the mean of the distribution, so the probability of finishing by that date is 50%.
Question 7: In CPM, 'negative float' on an activity indicates:
- The activity has extra time available beyond the project deadline
- The schedule cannot be logically completed without violating a constraint or deadline (Correct answer)
- The activity is not on the critical path
- The activity's duration was estimated too conservatively
Correct answer: The schedule cannot be logically completed without violating a constraint or deadline
Negative float means the current schedule violates a constraint (such as a must-finish-by date), and the project is already behind that target.
CST CPM & PERT Schedule Development 2
In PERT analysis, the Beta distribution is used because it: