CPM Method Problem

Can someone explain this problem to me? Why did they start at day 1 and not 0? Has anyone solved this problem using the 4-box method (as described in the CERM manual) and then solved the problem after accounting for the delay of activity E? I could really use some help on this problem.

Thanks in advance!

owillis

owillis,

This is a fairly straight-forward CPM problem with just one twist (which I doubt anyone would see on a morning question): you need to know what finish-to-finish lag means (the minimum amount of time that must pass between the finish of one activity and the finish of its successor, i.e. the Latest Finish of Predecessor <= Earliest Finish of Successor + FF). Without understanding this, you wouldn't be able to calculate the EF of D. However, once you get that, the rest of the forward pass easily falls in place. The backward pass is straight-forward. This problem also requires you to understand the difference between free float and total float.

Free float is the amount of delay which can be assigned to any one activity without delaying subsequent activities and Total float is the maximum amount of delay which can be assigned to any activity without delaying the entire project.

Regarding your first day is zero or one question... in this problem it doesn't matter (it won't change the float number). Nor does it affect project duration in days. It would, however, affect a question that asks on what day a certain activity starts or finishes. So if that's in the question, you need to decide on the convention used. The only benefit I know of to starting on day 0 is that the EF of the last activity becomes the project duration. But I don't think it makes sense to say there's such a thing as day 0 from a real-world perspective.

Bottom line take-away: Add lags during forward pass and subtract them during backward pass

Let me know where you got tripped up and I can walk you through it.

IlPadrino: Can you draw the completed network for me to check where I made a mistake.? I am not comfortable with my flow chart.

iykhan said:

IlPadrino: Can you draw the completed network for me to check where I made a mistake.? I am not comfortable with my flow chart.

Click to expand...

owillis posted the solution but now it seems to have been mangled.

owillis: can you fix?

IlPadrino said:

owillis posted the solution but now it seems to have been mangled.
owillis: can you fix?

Click to expand...

Thanks!

I am taking construction in the afternoon! HELP!!!!!!!!!!!!! I do not understand this problem either. I tried to use the 4 box metod but it dod not work. Can anyone explain this problem to me in a simplified manner.

4william said:

I am taking construction in the afternoon! HELP!!!!!!!!!!!!! I do not understand this problem either. I tried to use the 4 box metod but it dod not work. Can anyone explain this problem to me in a simplified manner.

Click to expand...

Where did you get stuck? The number of boxes isn't a "method". There are two common methods:

Activity on Node (AoN): AoN representation has the activitiy inside the node and the arrows represent the precedence relationships. This is used most often in conjunction with computer programs as they allow for easy data entry once precedence has been established. They are also convenient for determining start and finish times by hand.

Activity on Arc (AoA): AoA (also known as Activity on Branch) has the activity represent by the arrows themselves and the nodes represent the precedence as points in time where predecessors have been completed.

So... this is AoN (the number of boxes doesn't really change anything), and as I wrote above, it's fairly straightforward except for the finish-to-finish lag. I trust you're OK on the forward pass for A, B, C, F, and H.

Again, explain where you got stuck and maybe I or someone else can explain that part better.

IlPadrino said:

Where did you get stuck? The number of boxes isn't a "method". There are two common methods:
Activity on Node (AoN): AoN representation has the activitiy inside the node and the arrows represent the precedence relationships. This is used most often in conjunction with computer programs as they allow for easy data entry once precedence has been established. They are also convenient for determining start and finish times by hand.

Activity on Arc (AoA): AoA (also known as Activity on Branch) has the activity represent by the arrows themselves and the nodes represent the precedence as points in time where predecessors have been completed.

So... this is AoN (the number of boxes doesn't really change anything), and as I wrote above, it's fairly straightforward except for the finish-to-finish lag. I trust you're OK on the forward pass for A, B, C, F, and H.

Again, explain where you got stuck and maybe I or someone else can explain that part better.

Click to expand...

At this point, if you struggle with that CPM problem, I would suggest doing some very basic level cpm problems to get used to the overall method. You always start at day 1, and just add the duration to the early start time. AOA and AON carry the same principle, you just write the ES and EF times in different places. Just reviewing some examples should help immensely, then look at the lag stuff.

owillis28 said:

Can someone explain this problem to me? Why did they start at day 1 and not 0? Has anyone solved this problem using the 4-box method (as described in the CERM manual) and then solved the problem after accounting for the delay of activity E? I could really use some help on this problem.




Thanks in advance!

owillis

Click to expand...

I could not view the problem? where is the link or jpg file located?