Oliver 75 - 18th Question

[jyotimayank]

Question 18.

Start dates in the following network logic diagram are defined as early morning, finish dates are evening.
If tasks are scheduled to begin at early start date, what is true?


A. Activity B has a free float of 10 d.
B. Activity B has a total float of 10 d.
C. Activity A has a free float of 10 d.
D. Activity A has a total float of 10 d.

[jyotimayank]

The correct answer is B.

Apply the formula on all the activities
Applying the formula on activity B
Float = LS (Late Start) – ES (Early Start)
= 26 - 16
or
Float = LF (Late, Finish) – EF (Early Finish)
= 31 - 21
=10

This is how PMBOK® Guide Fifth Edition defines Total Float

“The amount of time that a schedule activity can be delayed or extended from its early start date without delaying the project finish date or violating a schedule constraint.”

So this is talking about flexibility we have at project level. Now in a network diagram, we can have multiple paths to reach the end. So this float talks about flexibility one path has as compared to others.
Simple formula to calculate total float is our usual formula i.e. LS (Late Start) – ES (Early Start) or LF (Late, Finish) – EF (Early Finish)

Free Float

“The amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint”

Simple formula to calculate Free Float is ES (of successor) – EF of current activity

PMBOK® Guide Fifth Edition defines Critical path method as

A method used to estimate the minimum project duration and determine the amount of scheduling flexibility on the logical network paths within the schedule model. This schedule network analysis technique calculates the early start, early finish, late start, and late finish dates for all activities without regard for any resource limitations by performing a forward and backward pass analysis through the schedule network. The critical path method is used to calculate the amount of scheduling flexibility on the logical network paths within the schedule model.

Refer to Page 176-178 0f PMBOK® Guide 5th Edition

For more insight of this topic refer to the following blogs

Blog: Comparison between Early Start as 0 Or 1 in Network Diagram
http://www.izenbridge.com/blog/comparis ... k-diagram/

Blog: What Is Float And How To Calculate Total & Free Float?
http://www.izenbridge.com/blog/what-is- ... ree-float/

[Kumar]

Hi Jyothi,

Thanks for your detailed explanation. Out of the answers even the ans A is correct becoz the Activity B has free float of 10d.

free float= ES of Activity D - EF of Activity B = 10d

Can you please explain why you have chosen only the total float of B (anws B), why not free float of B (ans A).

Thanks.

[manishpn]

Hi Kumar,

I agree with your understanding activity B has total as well as free float of 10.

you can also refer to our blog in this regards.

http://www.izenbridge.com/blog/what-is- ... ree-float/

[abhavisetty]

When we say "Total float" I assume it is at the Project level and "Free float" is at the Activity level. If my understanding is True is option A the correct answer ?

[saket]

Here is a blog on Total Float and Free Float

http://www.izenbridge.com/blog/what-is- ... ree-float/

some more threads you can explore for better understanding

viewtopic.php?f=3&t=5188&p=19335&hilit=free+float#p19335

viewtopic.php?f=3&t=3892&p=15170&hilit=free+float#p15170

viewtopic.php?f=11&t=2927&p=10459&hilit=free+float#p10459

[vikram_unde]

Free Float = The amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint

Free Float of Activity B is as below -

Free Float (Current Activity) = ES (Successor Activity) – EF (Current Activity) -1
Free Float (B) = 31 (D) - 21 (B) - 1 = 9

Mean, Activity B should finish on day 30 so that successor activity D can start on day 3. This will not delay activity D and also not violate scheduling constraint.