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Top 10 Project Manager interview questions (first part) -- All answers about project planning!

Have you sent a job application for a PM role? The interview questions asked by Google, LinkedIn, and Facebook recruiters do not really matter: what matters is the knowledge you need to give the right answers to any question! ]

So, stop reading hundredth of interview questions: it is a waste of time. Rather work on the key concepts (processes, frameworks, methodologies, templates, steps, and tools) described in this series of posts and you will be in a much better position the day of the interview. In particular, many questions are about project planning and, in this post, I will give you all the elements to understand and answer the most common questions.

The definitive resource to learn everything that I present in this post is the PMBOK: "the guide to project management body of knowledge". It's a big book and it's quite unlikely you can read and understand it in time for your interview. But there is good news! I will give you the main concepts you need to know, so, that you can answer the most basic project management / program management interview questions after only a few minutes of work!

Project planning is part of Project Management

If you want to be a project manager, the minimum is to know what project management is. Do you have a good definition in mind? No? Well, you should have one! 

The PMBOK gives a complicated definition of project management. Based on the experience I have gathered managing projects during almost 10 years, I prefer this one (my own ;)): 
"Project management is the process of initiating, planning, monitoring, executing and closing tasks to achieve specific goals under given resource, time, and quality constraints."

What's a critical path / a critical task? What's a PERT diagram? What's the slack / float time of a task?

The critical path of a project is the sequence of tasks that defines the completion date. If one of the tasks on the critical path is delayed by 1 day, the project will be delayed by 1 day (except if other tasks of the critical path finish earlier than planned and compensate this delay).

A task is not critical if it can be delayed without impacting the project completion date. We say that it has some "slack" or "float". The float of the task is the amount of time it can be delayed without affecting the project completion date (total float) or the start another task (free float).

Let's analyze the example in the figure below. I chose it because it is a common representation of project activities, named PERT chart. PERT stands for "Program Evaluation and Review Technique". It's a way to identify the critical path.

The milestones of the project are represented as nodes (10-50). The tasks (A-E) are the arrows between the nodes and they are labeled with the expected time required to complete them. You can see that the task E starts at milestone 30 and requires 2 months. To complete (milestone 50), the project requires tasks F, E, and C to complete. As you can see we need 4+3= 7 months to achieve tasks B and C, and also 7 months to achieve A, D, and F. But we need only 5 months to complete A and E.  Consequently, if I delay any task among (B,C,   A,D, F), the project will be delayed. They are the critical paths! However, I can delay E by two months without consequence for the project: the slack time for E is 2 months.

PERT Chart. Drawn in Adobe Illustrator - inspi...
A network diagram used for project planning. Inspired by a chart at Created by Jeremy Kemp. 2005/01/11 (Photo credit: Wikipedia)
The figure above is a "network diagram", the arrows are labeled with a duration.  In fact, a real PERT diagram is a bit more complex: the tasks are labeled with

  • The task's Early Start (ES) and Late Start (LS) date. The difference between the two: F= LS - ES +1  gives the task's float (F), which is also displayed near the task.
  • The task's duration (D)
  • The task Early Finish (EF) and Late Finish (LF) date. Clearly, you obtain the early finish date by adding the task duration to its early start date: EF = ES + D -1. Same thing for the Late Finish date: LF = LS + D -1 
In the above equations if you wonder why there is a -1 or +1, consider a simple task example:
  • ES = Day 1
  • D = 1 day
    • This leads to EF = Day 1. This means that the task ends the same day as it starts. EF = ES +D -1
  • LS = Day 5 (5 days later).
    • This leads to: F= 5 -1 +1 = 5. The float is five days, i.e., we can delay the task by 5 days without delaying the project completion date.

Pert diagram nakreslenĂ˝ v Microsoft Visio
Example PERT diagram, with the labels indicating (from top left to bottom right) Early start, Duration, Early Finish, Late Start, Total Float, Late Finish

What's the difference between the critical path method and the critical chain method (CCM)?

The critical path method does not account for uncertainty in task duration. So, either you overestimate the task duration to plan for worst case scenarios, or you will finish late... To solve this issue, the critical chain method adds "buffers" at the end of every chain. The buffers are empty tasks associated with a duration equal to the probable delays along the task chain. This way, the buffers will absorb any delay in the execution of the tasks and the project execution date will not change even if a task lags. 

How do we calculate the expected time for a task?

In the previous section, I have labeled a PERT chart with well-defined task duration. However, task duration are very uncertain in practice! So, how did we calculate task duration?

A task can complete very quickly in the best case and take a long time in the worst case (e.g., a key contributor breaks his legs in a car crash and needs 2 months sick leave). So, the calculation of the expected completion time for a task must take into account both optimistic case, normal case, and pessimistic case. Now, the question is how do you weight all the cases? The classical practice is to give 4 times more weight to the normal time expectation. This gives:
  • expected duration = (optimistic + 4* normal + pessimistic) / 6
For instance, let's consider a task which takes
  • 3 days in the optimistic case
  • 10 days in the pessimistic case
  • 5 days in the normal case
Then, the expected task duration is :    (3 + 4*5 + 10) / 6 = 33/6 ~= 5.5 days.

I you are asked for the differences between the critical path method (CPM) and the program evaluation and review technique (PERT), the answer is that the task duration is assumed to be known in CPM whereas PERT takes into account the uncertainty of task duration, as described in the above paragraph.

Ok, but... In practice, how do I calculate the optimistic / normal / pessimistic time for a task?

There are two ways to estimate the time needed for a task in the optimistic / normal / pessimistic case:
  1. Divide and conquer: split the task into small pieces, until you see small work element that you can estimate in terms of resources / costs / time required for completion. Then add up the time required for all the elements and you will have a clearer idea of the time required for completing your task. This method is called the "work breakdown structure (WBS)".
  2. Use expert knowledge, gathered through previous projects, for instance, to estimate the required time for the task. If you have already done 10 similar projects, you should have a clear idea of the complexity of each task. Otherwise, someone in your planning team might have enough experience on that kind of tasks.

How to complete a project faster?

The duration of a project is defined by its critical path. If you want a project to finish faster, you need to reduce the length of the critical path. This means, in turn, reducing the duration of the critical tasks. How do we do that? It's all a questions of resources: I'll tell you the secret -- there are only 3 ways to make a critical task complete faster.
  1. Reduce the task scope
  2. Reduce the quality of the tasks' results 
  3. Increase the resources (skills, people, money...) allocated to the task
  4. Run several tasks in parallel (fast tracking)
That sounds bad, isn't it? Either we produce crappy results, or we do not provide all results, or we cost a lot of money to the company? Well, no! You have not understood the key point! We have looked only at the critical path, but some other tasks have slack! So, we could take resources allocated to the non-critical tasks and reallocate them to critical tasks instead. That way we do not increase the cost of the project, but it will complete sooner! 

What's a Gantt diagram?

A Gantt diagram is a way to represent the sequence of taks required to complete a project, their duration, and their dependency. So, it's an alternative to the PERT diagram that I mentioned above. The Gantt diagram is practical because you can describe the tasks in more details in the figure directly, as the tasks are represented by rectangles.

In the figure below, you have two sequences of independent activities in red and blue. The sequence that takes the longest to complete is the critical path. MS project shows the slack time, which is quite practical: the black bars represent the slack time in the figures.

A Gantt chart created using Microsoft Project ...
A Gantt chart created using Microsoft Project (MSP). Note (1) the critical path is in red, (2) the slack is the black lines connected to non-critical activities, (3) since Saturday and Sunday are not work days and are thus excluded from the schedule, some bars on the Gantt chart are longer if they cut through a weekend. (Photo credit: Wikipedia)

What's a precedence diagram?

I have provided you a few examples of Gantt and PERT diagrams above. The precedence diagramming method (PDM) is a method to draw a simpler diagram, without task duration. This diagram just displays the dependencies among the tasks. For instance, take two tasks:
  1. Dress up
  2. Go to the postal office

The 4 Types of Task Dependencies for Project Planning

You do not want to go to the postal office naked. So, there is a dependency between the two tasks. The "dress up" task must be finished to start the task "Go to the postal office". There are 4 kinds of dependencies:
  • Finish to start (FS): the example above
  • Start to start (SS): task 2 cannot start if task 1 is not started
  • Finish to finish (FF): task 2 cannot complete task 1 is not finished
  • Start to finish (SF): task 2 cannot finish if task 1 is not started
The precedence diagram draws the tasks in rectangles and connects them with arrows labeled with the type of dependency. With our example it gives:
"Dress up"   ------- FS ------> "Go to the postal office"
Sometimes the precedence diagrams are complemented with the duration of the tasks and the starting date:
  • Early start date 
  • Late start date 
  • Early finish date 
  • Late finish date
To conclude, I advise you to read the PMBOK to learn more about project planning methodologies.


About Gilles


  1. Wonderful article. But recently if you are looking for a new project management job or if you might have asked for a promotion within your company then you might have heard about PMP credentials!!. It is true that a Project Management Professional (PMP) credential is one of the most sought certifications by employers and employees alike. For its detail information about a PMP certifications you can go through


    1. Tag: PM205A57. Let me share all of you about #5 Tips for Project Management Success,, I hope you enjoy it

      1. Plan your day using time management techniques

      As a project manager, time management skills are essential because you are dealing with a wide range of tasks that demand a quick turnaround time. Planning your day will go a long way in keeping you organized and increasing your productivity. Assist your task planning by using project management software which helps you track the work of you and your team.

      If you are not very tech savvy, a simple to-do list can also be a great organizational tool. Prioritize your most important tasks by putting them at the top of the list and less important ones at the bottom. Having a visual plan of your daily tasks helps to keep you on track and aware of time.

      Related post: Free ebook 104 secrets to become a great project manager

      2. Include stakeholders in important project conversations

      While you will have plenty of responsibilities regarding the project, don’t neglect your clients.

      Good communication is essential is keeping both parties informed of project progression, curtailing scope creep, and apprised of changing requirements. Some clients may have different expectations when it comes to communication, so make sure to establish the frequency and type of communication (like emails, phone calls, and face-to-face conversations) at the beginning of your project.

      Establishing communication expectations early helps alleviate stakeholder uncertainty about communication frequency and delivery.

      3. Regularly communicate with your team

      Daily team communication helps keep misunderstandings and unclear requirements under control. Keeping your team informed in every step of the project is essential to project management success.

      For example, a study published by Procedia Technology found that good communication skills were the cornerstone of project management. The study examined over 300 “construction project managers, architects, construction managers, engineers and quantity surveyors” and their successes and failures on various construction projects.

      4. Anticipate project setbacks

      Even the best-laid plans often go awry.

      Remember that even with a high amount of planning and attention to detail, your project may still encounter some challenges. Pay attention to complaints from stakeholders or colleagues, and other warning signs, like a missed deadline or cost overrun, that there may be a problem.

      Preventing a crisis will keep your project running smoothly, save you a lot of time, and keep you, your team, and your stakeholders confident in progressing with the project.

      Unfortunately not every complication can be avoided. Crisis management skills are essential for dealing with the unexpected. Project managers need to be flexible and pragmatic. Improvise and make sharp decisions when needed.

      Related post: 92 free project management templates

      5. Stay focused on the details

      A common problem project managers encounter is having the project aims not aligned with the organization’s objectives. A great project manager will strategize a plan for the project to lead back to the overall success of the business.

      Know your project’s scope by heart and avoid wandering outside of the project’s requirements. It’s too easy to get lost in minor details and forget what your focus is, so a well-planned project scope is essential for success.

      And final, you should use KPI to measure effectiveness of the project, here are full list: 76 project management KPIs

  2. Yeah its a good article. According to you what we project managers do is communicating. And a lot of this communication is done during project meetings. It can sometimes feel like you are running from one meeting to another and that your time is often wasted. Meetings don’t start on time, the issues aren’t dealt with, there is no agenda, there is no focus, nobody assigns any follow ups or tasks and of course then they also don’t end on time. An efficient project manager is required for the good management of a project. I think a project manager should PMP certified. Looking forwards to apply what I learned in PMP classes in my company.

  3. Hi there, awesome site. I thought the topics you posted on were very interestingThanks a lot for sharing your learning and experiences with your readers.It is a good source for the .PMP aspirants.

    Critical Path Method

  4. This is a great post. I like this topic.This site has lots of advantage. It helps me in many ways.Thanks for posting this again.
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  5. Tks very much for your post.

    Avoid surprises — interviews need preparation. Some questions come up time and time again — usually about you, your experience and the job itself. We've gathered together the most common questions so you can get your preparation off to a flying start.

    You also find all interview questions at link at the end of this post.

    Source: Download Ebook: Ultimate Guide To Job Interview Questions Answers:

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