Following is an illustration of a project network activity node that includes some information about activity D.

Given the information provided, what is the total float of activity D?



A. 2
B. 14
C. 16
D. 18

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HINT: Total float is calculated as the difference between the late start and the early start or between the late finish and the early finish.

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Answer and Explanation:
The correct answer is C.

To answer this question, the first step is to understand the meaning of the values displayed on the network activity node. The accepted convention is shown below, where:

• ES = early start
  
• EF = early finish
  
• LS = late start
  
• LF = late finish

The total float can be calculated using either one of the following two formulas:

• Total Float = LF - EF
• Total Float = LS - ES

To illustrate, we will use the first formula:

Total Float = LF - EF = 39 - 23 = 16

Here is the project schedule network activity node filled in with the correct answer for total float, 16:



Details for each option:

A. Incorrect. You might have gotten this answer if you merely subtracted 39 - 37 across the bottom or 23 - 21 across the top, but neither LF - LS nor EF - ES is the correct formula for float.

B. Incorrect. You might have gotten this answer if you subtracted diagonally 37 - 23, but LS - EF is not the correct formula for float.

C. Correct. There are two formulas for total float. One goes up the left (start) side: Total Float = LS - ES. The other goes up the right (finish) side: Total Float = LF - EF. Both get the same correct result of 16.

D. Incorrect. You might have gotten this answer if you subtracted diagonally 39 - 21, but LF - ES is not the correct formula for float.

Reference: A Guide to the Project Management Body of Knowledge (PMBOK^® Guide) – Seventh Edition, Project Management Institute Inc., 2021,
2.7.2.3 Baseline Performance

Process Groups: A Practice Guide, Project Management Institute Inc., 2023,
5.10 Develop Schedule
10 Tools and Techniques

Practice Standard for Scheduling - Third Edition, Project Management Institute, 2019,
2.2.1 CRITICAL PATH APPROACH
3.4.1.1 CRITICAL PATH

Additional resources:
www.project-management-prepcast.com/network-diagram