Question

Which one of the following is the excess of variable time over the activity time when all jobs start as early as possible?

• A. Dependent float
• B. Total float
• C. Independent float
• D. Interfering float

Hint:

Think of Independent Float as the "safest" float to use because it doesn't create ripple effects on other activities in the project schedule.

Answer 1

The Correct Option is C

Step 1: Understand the basic concepts of Project Scheduling and Float.
In project management, particularly with methods like CPM (Critical Path Method) and PERT (Program Evaluation and Review Technique), "float" or "slack" refers to the amount of time an activity can be delayed without affecting other activities or the project completion date. Step 2: Define the different types of float.
Total Float (TF): The total amount of time an activity can be delayed from its early start (ES) without delaying the project completion time. It is calculated as \( TF = LS - ES = LF - EF \), where LS is the late start, ES is the early start, LF is the late finish, and EF is the early finish of the activity. Free Float (FF): The amount of time an activity can be delayed from its early start (ES) without delaying the early start of any immediately following activity. It is calculated as \( FF = ES_{next} - EF_{current} \) or \( FF = TF - (ES_{next} - EF_{current}) \), where \( ES_{next} \) is the early start of the succeeding activity and \( EF_{current} \) is the early finish of the current activity. Free float can be used without impacting subsequent activities. Independent Float (IF): The amount of time an activity can be delayed from its early start (ES) without affecting either the early start of any immediately following activity or the late finish of any immediately preceding activity. It is calculated as \( IF = ES_{next} - LF_{previous} - Duration_{current} \). If this value is negative, the independent float is considered zero. Independent float is unique to an activity and its use does not affect any other activity. Interfering Float (InF): The difference between the total float and the free float. \( InF = TF - FF \). This float, if used, will affect the start of one or more subsequent activities. Dependent Float: This is not a standard, formally defined type of float in CPM/PERT. The other floats (Total, Free, Independent, Interfering) describe different ways an activity's schedule can vary. Step 3: Relate the question to the definitions of float.
The question asks for the "excess of variable time over the activity time when all jobs start as early as possible." Let's break this down:
"Activity time" refers to the planned duration of the activity.
"Variable time" in this context implies the flexibility or the amount of delay that can be tolerated.
"When all jobs start as early as possible" sets a specific condition for calculating this excess time.
Under the condition that all jobs start as early as possible, the excess time available for an activity without affecting the start of the next activity (and also not being affected by the finish time of the preceding activity) is the independent float. Step 4: Evaluate the options based on the definition of independent float.
Independent float represents the spare time within which an activity can be rescheduled without impacting its predecessors or successors, assuming both start and finish as early as possible. It's the time an activity can "vary" without causing any scheduling conflicts at its boundaries. Step 5: Select the correct answer.
The excess of variable time over the activity time when all jobs start as early as possible, such that it doesn't affect preceding or succeeding activities, is the independent float.