Need help with this question on Critical Path

Submitted by sunitaPMP on Mon, 12/17/2012 - 03:03

Can anyone help me with this question from Farnadales Guide(Q 3.16)

Can anyone tell me what is the critical path of this N/W diagram?

What is FS-2 and FS 4 upon the arrows ?

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sspawar

Mon, 12/17/2012 - 07:32

FS -2 has a meaning = Finish to Start dependency with 2days lead, (Dash between FS and 2 is a Minus Sign)


but


FS 4, without any sign have no meaning, it is typo error.


After referring answer from answer sheet, It is clear questioner (Mr. Farndale), wanted to write + (plus) sign there in between FS and 4, but it is missing, in question as well as in illustration.


+ (plus sign) means LAG


Critical path will be = A-D-G-(LAG)-K = 1+3+6+4(LAG)+2 = 16 days


others are =



  • A-B-H-k = 1+5+(9-2) +2 =15

  • ACEJK = 1+4+1+6+2 =14

  • ABEJK = 1+5+1+6+2 =15

  • ADGK = 1+3+6+2 =12

 


+ (PLUS) MEANS LAG


- (MINUS) MEANS LEAD


While solving such problem, always consider lead and lag as non scheduled activities (and write in between lag or lead),, like A-D-G-(LAG)-K = 1+3+6+4(LAG)+2 = 16 days


One problem of lead lag is also I have written in my blogspot (er-sspawar.blogspot.in), July 2012 5th number


Oliver Lehmann 75 also has excellent 2-3 illustrations, for better understanding.


 

sunitaPMP

Mon, 12/17/2012 - 20:22

Thanks a lot sspawar.

It really helps...

Also I have another question.We calcualte float after calculating ES,EF,LSand LF for all teh activities?Do we have any other method for it?

 

 

MAMPMP

Mon, 12/17/2012 - 20:37

Dear sunitaPMP, these are the questions that look complicated and difficult, take a lot of time looking at them and thinking how to find the answer, especially during the exam.

However these are the easiest ones...because, remember that the tasks within the critical path ALWAYS have zero (0) float, the example provides the float associated to the task and all of those with 0 float are part of the critical path.

sunitaPMP

Mon, 12/17/2012 - 20:57

Yes float for activities on critical path is zero.When activities on non critical path,calculating float for them is time consuming and error prone.So i was looking for any other quick way to find teh float without calculating ES,EF,LS and LF.

 

 

sspawar

Tue, 12/18/2012 - 03:37

Correction:

Last one non critical path written above is ADGK, will be ADJK. Activity J has shown SS (start to start) with F, greater one will be considered.

ADFJK === 1+3+(2-2+6 (ss)) +2 = ADJK

sunitaPMP

Wed, 12/19/2012 - 04:33

Hi sspawar,

I did not understand this above

ADFJK === 1+3+(2-2+6 (ss)) +2 = ADJK.

 What is ADJK in RHS?

 Also i did not understand the way you calculated ADJFK=1+3+(2-2+6 (ss)) +2

is not it should be 1+3+2+6+2?

 

Prakash999

Wed, 12/19/2012 - 05:06

 @SunitaPMP

there's a SS relationship between two activities on that path, and each has duration of 2 and 6. Effectivtely, while one activity starts and two days, second activity starts in parallel and takes 6 days . so they're both finished in 6 calendar days ( not 8 calendar days ). . so you need to ignore the duration of shortest activity while calculating this path.

Prakash999

Wed, 12/19/2012 - 05:06

 @SunitaPMP

there's a SS relationship between two activities on that path, and each has duration of 2 and 6. Effectivtely, while one activity starts and two days, second activity starts in parallel and takes 6 days . so they're both finished in 6 calendar days ( not 8 calendar days ). . so you need to ignore the duration of shortest activity while calculating this path.

sspawar

Sun, 12/23/2012 - 09:02

Few more youtube on lag lead and cpm example


http://www.youtube.com/watch?v=Whc0QHSuk28


http://www.youtube.com/watch?v=b2eKBP77P1I


http://www.youtube.com/watch?v=DdDzybQ_9vM