Float concepts in CPM: Which of the following statements about total float, free float, independent float, and interfering float are correct?
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AThe duration between the earliest start of a preceding activity and the latest finish of a succeeding activity can be viewed as available float in the chain
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BFree float is the time by which an activity can be delayed without affecting the start of any succeeding activity
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CIndependent float affects neither predecessor nor successor; it is the float available irrespective of other activities
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DInterfering float equals total float minus free float
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EAll the above.
Answer
Correct Answer: All the above.
Explanation
Introduction / Context:Float (slack) quantifies schedule flexibility. Proper use of float helps level resources and absorb uncertainties without delaying project completion. Different float types serve different management purposes.
Given Data / Assumptions:
- Total float TF = LS − ES = LF − EF.
- Free float FF = min(ES of successors) − EF.
- Independent float IF = max(0, ES of activity − LF of predecessor − duration).
- Interfering float = TF − FF.
Concept / Approach:Total float measures how much an activity may move without affecting project finish; free float preserves successors; independent float is the portion independent of both predecessors and successors; interfering float is the portion that, if used, will delay the early start of successors but not the project finish.
Step-by-Step Solution:Confirm total float via ES/LS or EF/LF relations.Compute free float using successor earliest starts.Compute independent float using predecessor latest finishes and own ES.Find interfering float as the difference: TF − FF.
Verification / Alternative check:Network calculations should show TF ≥ FF ≥ 0 and IF ≥ 0 (by definition floored at zero). Critical activities have TF = FF = IF = 0.
Why Other Options Are Wrong:All listed statements align with standard CPM definitions; therefore 'All the above' is correct.
Common Pitfalls:Using free float where preserving successor early start is not required; double-counting float when multiple successors exist; forgetting that independent float can be zero even when total float is positive.
Final Answer:All the above.