Critical Path Network problems on Breadth?

[maximus808]

I'm currently going over the construction portion of the CERN and is having difficulty with CPN problems. (Example 85-3).

Does anyone know if this is part of the breadth portion of the exam? Can someone explain the steps to figuring out the ES, EF, LS, and EF of the quadrants? I'm getting confused from the CERN page 85-11. Thanks

 

[maximus808]

nevermind, figured it out

 

[EnvEngineer]

I am afraid this is a large portion of the exam (October, it may change). You need to know it back ward and forward such as if task x were delayed 3 days how would the overall schedule be effected. There are some references available to help get more depth

 

[maximus808]

Wow, even in the breadth portion of the exam? I figured how to do a simple CPM problem filling in the different quadrants of ES, EF, LS, and LF based on an activity and duration but I have to do a few more problems maybe.

I'm choosing Transportation as my depth and I want to finish reviewing Construction so I can drill this section really hard. Thanks for your advice

 

[EnvEngineer]

Sorry in the breadth portion you need excavation volumes, production rates (3 monkeys working for 3 days...). I would plan on at least two CPM type problem where if the timing for one task is changed how will other tasks or the project be effected.

 

[Dexman PE]

Sorry in the breadth portion you need excavation volumes, production rates (3 monkeys working for 3 days...). I would plan on at least two CPM type problem where if the timing for one task is changed how will other tasks or the project be effected.

Or to identify the critical path for an established network. Once you figure out how the network is inter-related, most of these problems become quite simple. It's more of a matter of figuring out what the question is asking.

This is all explained very well in the "Project Management" Chapter (#81 in the 10th edition, not sure what chapter in the 11th).

 

[chess5329]

Sorry in the breadth portion you need excavation volumes, production rates (3 monkeys working for 3 days...). I would plan on at least two CPM type problem where if the timing for one task is changed how will other tasks or the project be effected.

Or to identify the critical path for an established network. Once you figure out how the network is inter-related, most of these problems become quite simple. It's more of a matter of figuring out what the question is asking.

This is all explained very well in the "Project Management" Chapter (#81 in the 10th edition, not sure what chapter in the 11th).

Dexman,

I have the 10th. edition, and there's nothing regarding, If an activity is delayed for 2 days how this fact affect the whole path?

or....I'm missing something!

Could you post an example?

Thanks

 

[Dexman PE]

Look at example 81.1 (in the 10th edition). It lists 8 different activities, each with a duration and predecessors. (I will modify this later in the post to answer your question)

Activity, duration, predecessor

A, 0 days (start)

B, 7 days, A

C, 6 days, A

D, 3 days, B

E, 9 days, B & C

F, 1 day, D & E

G, 4 days, C

H, 0 (finish), F & G

(dammit, my spacing disappears for the network below, but compare to the solution given in the book)

Basically, you use the info to create the network as shown in the solution. Start at the top and work your way down. You know that only activity A is the start. It's completion is needed before B and C can start:

B

/

A

\

C

Now you see that activity D only depends on B:

B - D

/

A

\

C

Activity E depends on both B and C:

B - D

/ \

A E

\ /

C

Activity F depends on D and E:

B - D - F

/ \ /

A E

\ /

C

Activity G only depends on C:

B - D - F

/ \ /

A E

\ /

C ---- G

Then H depends on F and G:

B - D - F

/ \ / \

A E H

\ / /

C ---- G

To find the critical path (not considering Early start, early finish, late start, late finish), you have to add up the duration of each path. This network has 4 paths: ABDFH, ABEFH, ACEFH, and ACGH. Using the durations given in the table you get 0+7+3+1+0=11 days, 0+7+9+1+0=17 days, 0+6+9+1+0=16 days, and 0+6+4+0=10 days respectively. Thus giving you a critical path of ABEFH=17 days.

To answer you question on how delays factor in:

Now let's say that something happens that delays the start of activity C by 2 days. The duration for activity C is now 8 days (6 days original duration + 2 days delay). You would then have to re-calculate each path that depends on C (ACEFH, and ACGH). Recalculating these two gives you: 0+8+9+1+0=18 days, and 0+8+4+0=12 days respectively. If C has a delay of 2 days, you see that the critical path has shifted to the ACEFH path for 18 days. Despite the fact that one activity was delayed by 2 days, the critical path was only delayed by one.

Knowing this, you can then see that if ONLY activity G was delayed by 2 days (only affects path ACGH), it's path is extended to 14 days. When compared to the original critical path of ABEFH at 17 days, you see that the delay for G has no effect.

Does this help?

 

[chess5329]

Look at example 81.1 (in the 10th edition). It lists 8 different activities, each with a duration and predecessors. (I will modify this later in the post to answer your question)
Activity, duration, predecessor

A, 0 days (start)

B, 7 days, A

C, 6 days, A

D, 3 days, B

E, 9 days, B & C

F, 1 day, D & E

G, 4 days, C

H, 0 (finish), F & G

(dammit, my spacing disappears for the network below, but compare to the solution given in the book)

Basically, you use the info to create the network as shown in the solution. Start at the top and work your way down. You know that only activity A is the start. It's completion is needed before B and C can start:

B

/

A

\

C

Now you see that activity D only depends on B:

B - D

/

A

\

C

Activity E depends on both B and C:

B - D

/ \

A E

\ /

C

Activity F depends on D and E:

B - D - F

/ \ /

A E

\ /

C

Activity G only depends on C:

B - D - F

/ \ /

A E

\ /

C ---- G

Then H depends on F and G:

B - D - F

/ \ / \

A E H

\ / /

C ---- G

To find the critical path (not considering Early start, early finish, late start, late finish), you have to add up the duration of each path. This network has 4 paths: ABDFH, ABEFH, ACEFH, and ACGH. Using the durations given in the table you get 0+7+3+1+0=11 days, 0+7+9+1+0=17 days, 0+6+9+1+0=16 days, and 0+6+4+0=10 days respectively. Thus giving you a critical path of ABEFH=17 days.

To answer you question on how delays factor in:

Now let's say that something happens that delays the start of activity C by 2 days. The duration for activity C is now 8 days (6 days original duration + 2 days delay). You would then have to re-calculate each path that depends on C (ACEFH, and ACGH). Recalculating these two gives you: 0+8+9+1+0=18 days, and 0+8+4+0=12 days respectively. If C has a delay of 2 days, you see that the critical path has shifted to the ACEFH path for 18 days. Despite the fact that one activity was delayed by 2 days, the critical path was only delayed by one.

Knowing this, you can then see that if ONLY activity G was delayed by 2 days (only affects path ACGH), it's path is extended to 14 days. When compared to the original critical path of ABEFH at 17 days, you see that the delay for G has no effect.

Does this help?

Awesome! mi friend, you already clarify a big mistake I did last test. Eventhough this is not explain in the CERM this way; it is very good, how you applied your knowledge to this!

This really will help all of us in this forum willing to take this coming test!

Using the same problem or other problem......could you explain when we have Free Float and Total Float?

Thanks again for the time you dedicate to this,

Regards,