Network planning (PERT/CPM): understanding a dummy activity In a project network diagram, what is a “dummy activity” used for, and how is it represented visually?

Introduction / Context:
Project scheduling with PERT/CPM frequently requires representing logical precedence accurately. A special construct called a dummy activity is introduced to maintain correct relationships among real activities without implying extra work. This question checks recognition of the purpose, properties, and standard drawing convention of dummy activities.

Given Data / Assumptions:

• We are working with classic arrow-on-activity (AOA) networks.
• The network must reflect correct precedence and avoid false parallelism.
• Dummy activities serve only for logic, not for work execution.

Concept / Approach:
In AOA networks, each activity is an arrow and each event is a node. Sometimes two different activities share the same start and end events, or a particular sequencing must be distinguished. A dummy activity (a dotted arrow) is inserted to preserve uniqueness of activity representation and to encode correct precedence when required by the logic but without adding work.

Step-by-Step Solution:
Identify the role: logic maintenance only, no physical work.Recognize standard notation: drawn as a dotted/broken arrow between events.Attribute durations/resources: set to zero; it consumes no time, manpower, or cost.Conclude: all listed statements (dotted line, artificial, no time/resources) are true.

Verification / Alternative check:
Compare early/late times: introducing a dummy does not change the critical path or total duration; it merely ensures correct dependency representation.

Why Other Options Are Wrong:
Any option implying a real duration or resource load contradicts the definition of a dummy activity.

Common Pitfalls:
Confusing a dummy with a milestone; a milestone is an event (node), whereas a dummy is a zero-duration arrow used to model logic.

Final Answer:
All of these