Activity F will start when activity E has reached 40% but there is no incentive of finishing activity E as there is nothing attached to its completion. The relationship is for its 40% completion so that activity might be get lost.
Dangling activities (also known as dangles) are loosely-tied activities in project schedules. They are activities with either open start dates or open end dates. All activities, except the first activity of a network, need to have a predecessor; otherwise, they will have open start dates.
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