In PERT and CPM network the dummy activity

Explanation:

Dummy activity: 

• While establishing the relationships and drawing the network diagram sometimes it so happens that there does not exist any real activity between two events but an event cannot be said to have occurred unless and until some other event has occurred. Such cases are shown on the network diagram as dummy activities.
• The purpose of dummy activity is to maintain the logic of a network diagram.
• Since no real activity takes place between two such events, the dummy activity does not consume any resources.
• It also does not consume time duration.
• Dummy activities are used only in case of absolute necessity. 
• The symbolic representation of dummy activity is shown as-

Here, the dummy activity is between 2 - 3 which is given by dotted lines.