Duration of activity

Submitted by svsatheeshkumar on Wed, 07/10/2013 - 12:36

 An activity has a ES of 3 days, LS of 13 days, EF of 9 days and LF of 19 days. What is the duration of this activity ?

a) 3

b) 6

c) 7

d) 10

 

Given Answer : B

What is the correct formula to use ?

Duration = Early Finish - Early Start  + 1  (Assuming 1 as start of the day)

 = 9 - 3 + 1 = 7

Duration = Early Finish - Early Start          (Assuming 0 as start of the day)

 = 9 - 3 = 6

 I am confused which formula is the correct one to use in this scenario ?  Would like to hear from experts !.               

 

 

 

 

 

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cnppmp1's picture

cnppmp1

Wed, 07/10/2013 - 14:58

Use the Zero method or 1 mehtod it should be 6.

In 1 method you use adding 1 while you are calculating the ES for the successor activity (in case of multiple activities duration or project duration), not for calculating duration of the activity itself.

Hope this clears your doubt.

 

Regards

CN Patil

svsatheeshkumar

Tue, 07/16/2013 - 22:58

 Hi CN,

So if the question did not mention anyting about the start day of the activity, should we assume start day as 1.

Regards

Satheesh

 

ramzy's picture

ramzy

Thu, 07/11/2013 - 01:19

Hi CN,


I would like to know when to use which formula?
The questions is asking about Duration but did not mention anything about the Start activity duration if it's 1 or 0.

My initial answer was D.10 - this is because i used below formula ;

    1. LS-ES : 13-3 = 10
    2. LF-EF : 19-9 = 10

I also come to know that the formula to calculate Float/Slack is ;

    1. LF-LS
    2. EF-ES

However, i'm confused on how and when should i use the 'Standard' formula and when should i use the 'Forward pass' / 'Backward pass' formula.

Thank you for your time.

 

Regards,
Ram

ppalkonda1975

Tue, 07/16/2013 - 23:22

 You do not need to calculate float or slack..the above formula you are using is for float calculation

they are asking duration..which is EF - ES. which would be 6

 

ramzy's picture

ramzy

Wed, 07/17/2013 - 07:49

Hi,

Thank you for your response.

However, when i calculate this method manually, the Earliest work can begin is on Day 3 and the Latest finish day will be Day 9.

That said, it will be Day 3, Day 4, Day 5, Day 6, Day 7, Day 8 & Day 9 which is 7 days in total.

Not sure if this is correct logically.  I'm confused.

bkthakkar

Wed, 07/17/2013 - 06:07

Hope your determination of duration  in the scenario of ES,EF,LS and LF is clarified with the above explanation.


with regard to the usage of Forward and Backward Pass, this is required to determine the float /slack available in the particular activity in the network diagram.


By calculating float, u will be able to either fast track or crash the project depending on the project requirements so that project objective is attained.


Trust i have clarified your doubts


Bhavesh

ramzy's picture

ramzy

Wed, 07/17/2013 - 07:53

Thank you Bhavesh, as much as it does clear my doubt, i'm confused with when to use which formula.

Can i conclude that

    1. To calculate Duration, it will always be EF-ES OR LF-LS?

    2. To calculate Float/Slack, it will always be LF-EF OR LS-ES?
 

bkthakkar

Wed, 07/17/2013 - 08:24

yes

ramzy's picture

ramzy

Fri, 07/12/2013 - 13:53

Hi, anyone to answer my confusion above?

I appreciate your responses, thank you.