TOPIC: CP, Lead and Lag problems.

Hi Cornelius,

I was doing Sample Tests and found this question misleading..I thought CP is the longest duration of the network diagram, but your answer to this question said minimum duration, please clarify by looking at the attached doc.

Also, it would be great if you can give me more examples on Lead and Lag to have a better understanding for the exam. If you use visual diagrams/network diagram/CP to explain in this forum, that would be great.

Thanks!

Sorry, couldn't attach the document, but your example will be just fine.

As a recap for everyone else, I took the "offline" conversation that I had with Malcolm before he posted his question in our forum, and wrote the following PMP Exam Tip about it:

A student of ours who was answering questions in our PMP Exam Simulator ( www.pm-exam-simulator.com ) recently asked for an explanation of the following question he came across:

What is the Critical Path?

A.) Maximum project duration
B.) Minimum project duration
C) Total slack
D) Total float

He immediately realized that answers C and D are completely wrong and did not consider them. But then he fell into the “trap” that this question was setting up and selected “A.) Maximum project duration” as the correct answer. But the correct answer is in fact “B.) Minimum project duration”. Let me explain why.

First let’s acknowledge that the question is intentionally worded and phrased in this way. It's not meant to mislead, it's meant to make you think about what the critical path truly is.

That much said, you will probably remember from your studies that the critical path is the longest duration that you currently have in your schedule network diagram. But this does NOT mean that the critical path is the maximum duration that your project will/could have.

Let's look at an example and let’s say that our network diagram currently says that our critical is 30 days long. Is that the maximum that our project will take? No... it's the MINIMUM.

The critical path says that if everything goes as planned and we have zero delays, then we will be done in 30 days. But if there is just one task on the critical path that gets delayed by 2 days, then our critical path (and project duration) will increase to 32 days.

Therefore the critical path is not the MAXIMUM duration that we can expect on our project. It's the MINIMUM. (But only if all goes well).

Malcolm,

Here are some examples for lead & lag for you:

LEAD: When baking a cake you usually have to pre-heat the oven to a certain temperature. So if you did everything in sequence you would bake as follows: 1) get mixture ready 2) turn on oven 3) wait for 20 minutes until it's hot 4) put everything into the oven to bake. But of course what most people do is they realize that they can start the oven early, so that they don't have to wait. So in essence they put a "lead" onto the activity of starting the oven. They realize "I will be finished with the cake mix in about 20 minutes. Better start the oven now...". In this way the oven is hot, by the time the cake is ready to go in. So a lead is here to start an activity early.

LAG: Would you byte into the cake as soon as you take it out of the oven...? No. You put about a 90 minute lag in between "take finished cake out of oven" and "eat cake". In this way we use a lag to start an activity delayed (later) an not immediately after the predecessor is ready.

I also recommend taking a look at the following articles that describe these a bit more:

www.project-management-prepcast.com/inde...ds-lags-and-hammocks

www.passionatepm.com/blog/lead-versus-lag-pmp-concept-15

Thanks Cornelius for your input on Lead and Lag. Are there any good sample tests for Leads and Lags to clear doubts?

Malcolm,

You mean PMP exam sample questions? Not to my knowledge, because frankly, the concept is rather simple. A lead makes a task start sooner and a lag makes it start later. Not much to "test" here...