Project Management Course

George Mason University


Information Technology
Project Management


Critical Path Method

This lecture reviews the critical path method.  Project management software generally calculate the critical path, so most students do not need to do so by hand.  This lecture provides you with insight on how the software establishes the critical path.


  1. Understand calculation of earliest start and finish times
  2. Calculate the slack time for each activity
  3. Identify the critical path
  4. Examine impact of splitting an activity
  5. Communicate schedules to others

Assigned Reading

  1. The critical path methods as a quality tool.  More


  1. Lecture on critical path method.  Slides  Listen►  SWF► You Tube 1► You Tube 2►  Arabic 1►  Arabic 2►
  2. Lecture on estimating duration of an activity  Slides►  Listen►  SWF►  WMV►  Arabic►

What you know?

Advanced learners like you, often need different ways of understanding a topic. Reading is just one way of understanding. Another way is through writing about what you have read.  The enclosed assessment is designed to get you to think more about the concepts taught in this session. 

  1. What is the relationship between slack and earliest start time?
  2. What is the relationship between critical path and slack time of activities?
  3. What is calculated in the forward pass?
  4. What is calculated in the backward pass?
  5. What charts are used to communicate a schedule?
  6. What is estimate-talk-estimate and how much more accurate is it from simply having a discussion and then estimating the duration of an activity?

Please send an email to your instructor with your responses to the above questions.    Make sure that the email subject line includes the course number, topic name and your name, otherwise it will not get to the right place.  If you wish to receive a receipt that the instructor has received your email, you may request the receipt from your email program.  Please respond to all of the questions within the same email.  Do not attach any files.  Keep a copy of all your emails to the instructor till the end of the semester.  Email►


Rapid Analysis

  1. Three experts have estimated the duration of an activity to be 5, 7 and 10 weeks.  After discussion they have revised their estimates to 5, 8 and 9 weeks.  What is your estimate of the duration of this activity?

  2. Select two informants to interview (could be classmates), use the estimate talk estimate procedure, find out optimistic, realistic and pessimistic estimates of how long it takes to park a car on or near campus.  Describe who you interviewed, what were their first set of estimates, what was discussed, and what were their subsequent estimates. 

  3. In the following three project network, calculate the earliest start and latest start for each task.  Task are on nodes.  Duration of tasks are on arcs following each task.


  4. Given the following table of activities and precedents, calculate the earliest and latest start and finish times of the various activities.  Report the slack for each activity.  Indicate the activities on the critical path.


    Description of Activity

    Immediate Precedence Duration Earliest Start Earliest Finish Latest Start Latest Finish Slack
    A Obtain list of patients   2 weeks 1/1/2009        
    B Sample patients A 1 week          
    C Print survey tool   3 weeks          
    D Mail survey tool B, C 4 weeks          
    E Collect early responses D 1 week          
    F Collect late responses E 3 weeks          
    G Analyze data E 2 weeks          
    H Report findings F, G 1 week          


  5. Calculate the start and end dates for the following tasks in a healthcare construction project that is supposed to start on January 1st, 2009.  Show which activities are on the critical path.

WBS code

of Activity

Pessimistic Realistic Optimistic Start End Critical
1 Strategic plan phase   9 months 8 months 6 months 1/1/2009    
2 Project initiation phase 1 Depends on duration of sub-tasks      
2.1.    Team formation   3 months 2 months 1 month      
2.2.    Master facility plan 2.1 8 months 7 months 6 months      
2.3.    Space programming Finish with 2.2 9 months 7 months 6 months      
2.4.    Land acquisition analysis 2.2 6 months 4 months 3 months      
2.5.    Project budget & schedule 2.2 5 months 2 months 1 months      
2.6.    Joint venture analysis 2.1 5 months 2 months 1 months      
3 Building design 1, 2 Depends on duration of sub-tasks      
3.1.    Facility design   9 months 7 months 6 months      
3.2.    Equipment planning 3.1 6 months 4 months 3 months      
3.3.    Regulatory approvals 3.2 4 months 2 months 1 month      
4 Construction phase 3 9 months 6 months 5 months      
5 Occupancy 4 3 months 2 months 1 month      




  • Critical path method using Excel  More

This page is part of the course on Project Management.   This page was last edited on 01/31/17 by Farrokh Alemi, Ph.D ©Copyright protected.