Critical Path question.

Submitted by Samir on Wed, 03/28/2012 - 08:37

Q. Based on the following, if you need to shorten the duration of the project, which activity would you shorten?


Activity             Preceding Activity          Duration in months


Start                         None                             0


A                               Start                               1 


B                               Start                               2


C                               Start                               6


D                               A                                     10


E                               B,C                                 1


F                                C                                    2


G                               D                                    3


H                               E                                     9


I                                 F                                    1


End                          G,H,I                               0


 


a. Activity B


b. Activity D


c. Activity H


d. Activity C


Could someone please tell me correct answer with justification.


 


 

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projmanpro

Wed, 03/28/2012 - 11:56

The longest path here is START - C-E-H-END. Since C has 6 days while H has 9, choice should be H - to compress.

Samir

Wed, 03/28/2012 - 12:01

Thanks, I also felt the same. However, as per Rita's book the answer is 'D' i.e Activity C.:)))))

projmanpro

Wed, 03/28/2012 - 12:14

What is Rita's explanation then? i can compress 6 days for activity H, so i would have 3 days for activity H; while in Actvity C, to compress the same 6 days will give activity C = 0 days which means you are deleting activity C(it is not a milestone) - in this case this is not logical, taking into consideration that it is not mentioned in the question how many days to compress, so i would assume the maximum number of days i can compress.

The only valid reason i could see to choose ACtivity C is that it is an earlier activity, which means there is less risk, rather than compressing a later activity.

Samir

Wed, 03/28/2012 - 12:33

Her explaination is ..


'In this case, both activity C and activity H are on the critical path. If you have a choice, all things being equal, chose the earlier option. Therefore, C should be compressed.'


However, I am not sure what she means by 'all things being equal'. Duration is not equal in this case.


 

projmanpro

Wed, 03/28/2012 - 12:50

Ah.. You see, Rita considers my second opinion i stated that - the only valid reason we could choose Activity C is that it is an earlier activity and compressing earlier activities could have less risks than late activities. However, the question facts are not complete for us to decide that it should be C. As what i said, given the facts in the question, me as a PM have the options. The reality are: I can compress both C and H. If there is only an choice C&H - then this could be the best asnwer. But since there is no, the examinee may assume, to compress the maximum and in this case H has more days to be compressed (considering that the number of days to compress is not also mentioned). 

I hope questions worded like that would not appear in the actual PMP exam as for me, the question is like - "How could you derive the quadratic equation?" -that everyone could have his own correct approach of derivation.

 

 

twenty20

Wed, 03/28/2012 - 12:55

@projmanpro: How can you compress 6 months for activity H? since the difference with the next critical path is just 2 months, I guess the max you can compress is 2 months to get any benefit from compression.


Start-ADG-End -14 --> Next Critical Path
Start-BEH-End - 12
Start-CEH-End - 16  --> Critical Path
Start-CFI-End   - 9


I also opt to compress H, bur Rita's explanation makes sense since 'C' is earlier in the project and will not impact the later activities.


Cheers, Naveen

projmanpro

Wed, 03/28/2012 - 13:00

@twenty: that is only an example. Yes, i agree the maximum compression must be 2 to be exact.

twenty20

Wed, 03/28/2012 - 13:10

@Projmanpro


Thanks for clarifying. I just finished studied Time Management last week and wanted to check whether my calculation was correct. :-)


Cheers Naveen

Samir

Wed, 03/28/2012 - 13:14

Thanks guys.

pri_july

Wed, 03/28/2012 - 13:52

As Activity C is only common point in 2 paths.


If we compress Activity H, and later due to lag or due to some circumstances, duration of Activities F and I increases, then there is a possibility duration of Start-C-F-I-End equals to duration of Start-C-E-H-End, thus giving rise to 2 critical paths (risks).

Hence, it's better to compress C to avoid any risk in future.