Backward Pass

5 minutes 5 Questions

In contrast to the forward pass, the backward pass is a project network diagram technique used to determine the late start and late finish dates of unfinished activities. It works by moving backward through the network diagram. This method helps in pinpointing the tasks that could be delayed, without affecting the project's end date, which is critical in project scheduling and risk management.

Guide: Understanding and Answering Questions on the Backward Pass Concept

The Backward Pass, a crucial part of the Critical Path Method (CAPM), is fundamental in project management.

What is the Backward Pass?
The Backward Pass is a process in project management for calculating the late start and late finish dates for uncompleted activities by working backwards through the project schedule from the project’s end date.

Why is it important?
It establishes the latest possible times that activities can start and finish without delaying the project. It helps to identify the tasks with zero float called the 'critical path'. These are the tasks that cannot be delayed without affecting the project's finish date.

How it Works?
The process begins at the end point of the project. The late finish dates of each activity are set to the earliest of its successor's late start date, and the process works all the way back until the start of the project.

How to Answer Questions on Backward Pass in an Exam?
It's important to first understand the question: determine which activities are being referenced, and the specific information asked about these activities. Use the formulas associated with backward pass to find out the late start and late finish dates. Always remember that late start is equal to late finish minus the task duration plus one. And, late finish is the earliest late start of all successor activities.

Exam Tips:
  • Read the question thoroughly and understand what is specifically asked.
  • Sketch a network diagram if one is not provided.
  • Do not forget to calculate using the right formula.
  • Practice different network diagrams before heading into an exam.
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CAPM - Backward Pass Example Questions

Test your knowledge of Backward Pass

Question 1

In a project with activities A-B-C-D-E, each taking 3 days, the project must finish in 18 days. If activity C finishes on day 9, what is the Late Start (LS) for activity E?

Correct Answer: Day 13

The correct answer is 'Day 13'. Let's break down the problem step by step:

  1. The project has 5 activities (A-B-C-D-E), each taking 3 days.
  2. The total project duration is 18 days.
  3. Activity C finishes on day 9.

To find the Late Start (LS) for activity E, we need to work backward from the project end date:

  1. Activity E takes 3 days and must finish by day 18.
  2. Therefore, the Late Finish (LF) for activity E is day 18.
  3. The Late Start (LS) for activity E is 3 days earlier: 18 - 3 = 15.

However, we need to consider the given information about activity C:

  1. If C finishes on day 9, and each activity takes 3 days, activity D can start on day 10.
  2. Activity D will finish on day 12 (10 + 3 - 1).
  3. Activity E must start immediately after D to meet the project deadline.

Therefore, the Late Start (LS) for activity E is day 13.

The other answers are incorrect:
- Day 15 is too late and would cause the project to exceed its 18-day limit.
- Day 12 is impossible as activity D is still in progress.
- Day 10 is too early, as activities C and D haven't been completed yet.

Question 2

In a product development project, tasks are scheduled in sequence A-B-C-D. Task A has a duration of 4 days, B has 5 days, C has 3 days and D takes 2 days. The project must be completed in 14 days. If task B is completed on the 6th day, what would be the Late Start (LS) of task D?

Correct Answer: Day 12

Late Start (LS) of task D is the latest time that task D can start without delaying the project. If task B finishes on the 6th day, then task C, with a duration of 3 days, will finish on the 9th day. This means, Task D can start on the 10th day at the earliest. However, since the project must be completed in 14 days and Task D only takes 2 days, Task D can start as late as the 12th day without delaying the project. If Task D starts on the 10th day ('Day 10'), 9th day ('Day 9'), or 11th day ('Day 11'), it would either be too early or risk not finishing the project on time. Therefore, 'Day 12' is the correct answer.

Question 3

In a project, task P (4 days), Q (3 days), R (2 days), and S (2 days) should be completed sequentially. If Q completes on the 7th day, when will S be completed?

Correct Answer: 11th day

Task Q ends on the 7th day. Therefore, Task R, which takes 2 days, would finish on the 9th day (7 days + 2 days). Subsequently, Task S, also requiring 2 days, would end on the 11th day (9 days + 2 days). So the answer '11th day' is correct. The answer '12th day' is incorrect because it adds an extra day to the project timeframe. The '10th day' answer also incorrectly assumes that Task S will be completed in just 1 day. Similarly, '9th day' is wrong as it refers to the end of Task R, not Task S.

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Other Critical Path Method concepts

Activity SequencingCritical PathEarly Start and Early Finish DatesFloat or SlackForward PassLate Start and Late Finish DatesLead and Lag TimeProject DurationProject Network Diagrams
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