PMP Float Question

Discussion in 'PMP' started by Shan109, Aug 17, 2017.

  1. Shan109

    Shan109 Active Member

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    The ES of an activity is 2 days, and the duration of the activity is 5 days. The LF for the activity is 8 days. What is the total float for this activity?
    6 days
    3 days
    1 day
    5 days
    Explanation:
    We can calculate float using the formula EF=ES+D=2+5=7 and LS=LF-D=8-5=3. The formula for Total float is LS-ES or LF-EF. The answer is 1 day.

    The answer is assuming using ZERO method but PMI standard is to use ONE standard, wherein EF = ES + DURATION - 1

    Can someone please clarify?
     
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  2. tim jerome

    tim jerome Well-Known Member
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    Actually Day-0 notation and Day-1 notation are both usable. It depends on what you want to discuss.

    • Day-0 looks at duration - at any point in my schedule, how much duration has occurred? You merely add up the durations of the activities.
    • Day-1 looks at your schedule. You start beginning of day 1, and end at the end of the finish day. Notice also, where there is not duration between one activity and the next for Day-0, in Day-1, you increment the day. This makes sense since you end at the end of one day, and start the beginning of the next.
    The formulas for Day-0 are simpler to memorize, but many PMs from a formal scheduling background gravitate to Day-1. Both are usable for the exam.

    Both, if applied will give you the appropriate float. Again, both are usable for the exam. Just remember - starting with 0, I am discussing duration, and starting with 1, I am discussing the schedule.
     
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  3. Shan109

    Shan109 Active Member

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    Thanks a lot for taking your time to provide a detailed clarification. Much appreciated.

    You mentioned that the answer should be the same using both ZERO and ONE methods. However if I use the ONE method, I get a different answer:

    Using ONE Method:

    EF = ES + Duration - 1
    EF = 2 + 5 - 1 = 6
    Float = LF - EF = 8 - 6 = 2, which is different to the float of 1 using ZERO method.

    I guess the question is how would I know which method to use. I think you have tried to clarify this in your response that if there is no duration then I could use ONE method but I don't really get that.

    Thanks in advance
     
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  4. tim jerome

    tim jerome Well-Known Member
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    I just wrote a blog post on this among a couple other items. Go to the first question, and look to the graphic...
    https://www.simplilearn.com/pmp-questions-by-students-article

    Now, find the two schedule diagrams; the left one is Day-0, and the right one is Day-1. Look to Activity C. Note what was stated - Day-0 is discussing duration (where am I in work) and Day-1 is discussing schedule (where I am on the calendar). Now, walk through the generation of ES, EF for both models. Walk through the LF, LS numbers, and note the formulas used.

    Now look at the calculation of float.

    Again, when you analyze the diagram, it is really your preference. I would recommend you stick with Day-0 and not worry about Day-1 until you enter an organization that is very focused on schedule management.
     
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  5. Shan109

    Shan109 Active Member

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    In your activity A, using ONE method in the first topic, you have shown EF to be equal to 3. But if I use the formula EF=ES+Duration-1, this would give me 2 = (1+2 -1). Can you please clarify my understanding? Also you mention that float is same regardless of which method we use, but in my question above the float is not the same using the two methods.

    The ES of an activity is 2 days, and the duration of the activity is 5 days. The LF for the activity is 8 days. What is the total float for this activity?
    6 days
    3 days
    1 day
    5 days
    Explanation:
    We can calculate float using the formula EF=ES+D=2+5=7 and LS=LF-D=8-5=3. The formula for Total float is LS-ES or LF-EF. The answer is 1 day.
     
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  6. tim jerome

    tim jerome Well-Known Member
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    Dissecting this question, I see the problem. There is no way to determine the 'correct' LF. It may be after day 8, but it also may be after day 6. that 8 days is 'how much duration has occurred' if you are looking at Day - 0.

    You need a successor's LS to understand the balance. Succinctly, once you have related this activity in schedule to the other activities around it, you'll see the float calculated in both manners equalling eath other. Try it out - build a short diagram and see if you can force your schedule float to not be equal to duration float.

    Remember, Day-1 is 'where on the schedule', not how much duration, but float is indeed float.
     
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  7. Shan109

    Shan109 Active Member

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    Hi Tim
    I have done an exercise to calculate free float and total float for the task, by adding an imaginary successor task.
    (see attached).

    My conclusion is that Free Float is the same using both (ZERO and ONE) methods.

    However the total float is different depending on which method is used.

    PS: I wasn't sure what you meant by Duration Float and Schedule Float.
     

    Attached Files:

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  8. tim jerome

    tim jerome Well-Known Member
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    I confused you by bringing up duration float and schedule float. I was trying to reference float as it has to do with duration and float as it has to do with schedule. Perhaps for the discussion, it's not needed.

    You've brought up total compared to free float. In effect, we've been talking about free float for our examples. When you discuss total float, you need to consider the end of the project - you can't merely separate a segment of the network diagram.

    For task 2 on your network diagram, is it on the CP? If so, it has no float. If not, it has float. If Task1 does not lead to a CP activity directly, free float may indeed not equal total float.

    Please remember - we were initially discussing general float as it refers to analysis under Day-0 and Day-1 notation. If you want to talk about Free and Total float under these circumstances, it will be a much longer and deeper discussion.
     
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  9. Shan109

    Shan109 Active Member

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    Actually I shouldnt have included free float as that was not part of our discussion in comparing the one and zero methods. I just added it for completeness of analysis and I am not comparing total float to free float.

    So back to the question. Just sticking with Float (not free float) - when we use the two methods we get different answers so how do we know which method to use and why. My trainer told me that PMI and American standards prefer to use ONE method and British standards prefer to use zero method. I don't know if I agree with him but the point is that the two methods result in different answers and that is a source of confusion
     
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  10. tim jerome

    tim jerome Well-Known Member
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    Stay with Day 0. After you pass the exam, use exercise 9 as a template and look for further anomalies. I'll do the same.

    Regards,
     
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  11. Shan109

    Shan109 Active Member

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    Hi Tim. Thanks for your advice. I had my exam on Monday 21 August which I thankfully passed and interestingly there was a question that required calculation of forward pass and backward pass to calculate float and free float. I used the ONE method and am pretty sure I got the right answer. I was tempted to try the ZERO method as well to check if the answer was the same but was running out of time so didn't bother.
    Anyway, thanks for all your help and prompt responses to my questions
     
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  12. tim jerome

    tim jerome Well-Known Member
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    Thank you. You earned the credential. It's through great effort we create big change.
     
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