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
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/