Question

Painting is one of the activities in a construction project. For the painting activity that takes 6 days, both the total float and the free float are zero.
Which ONE of the following is TRUE for the painting activity?

• A. Painting is a dummy activity.
• B. Painting is a non-critical activity.
• C. The start of painting activity can be delayed without causing delay in completion of the construction project.
• D. The start of painting activity cannot be delayed without causing delay in completion of the construction project.

Hint:

Zero total float means an activity lies on the critical path, so recall what that implies about delaying its start.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We are told that the painting activity takes 6 days and that both its total float and free float are equal to zero.
We need to decide which statement correctly describes what a zero float means for this activity.

Step 2: Key Formula or Approach:
Total float of an activity is the maximum amount of time the activity can be delayed without delaying the entire project.
\[ \text{Total Float} = LS - ES = LF - EF \]
Here \( ES \) and \( EF \) are the early start and early finish, while \( LS \) and \( LF \) are the late start and late finish of the activity.
Whenever total float equals zero, the activity has no room to slip and is called a critical activity, sitting on the critical path of the project network.

Step 3: Detailed Explanation:
Option (A), painting is a dummy activity: a dummy activity always has zero duration and is only used to show logical dependency in the network, but painting takes a full 6 days, so it cannot be a dummy activity, this option is false.
Option (B), painting is a non-critical activity: an activity is critical exactly when its total float is zero, since painting has zero total float it must be critical, not non-critical, so this option is false.
Option (C), start can be delayed without delaying the project: this is the definition of having positive float, but painting has zero float, meaning there is no slack at all, so delaying its start would directly push the project finish date later, this option is false.
Option (D), start cannot be delayed without delaying the project: since \( LS = ES \) when total float is zero, there is no gap between the earliest and latest possible start time, any delay in starting painting immediately eats into the project's overall schedule, this option is true.

Final Answer:
Zero total float means painting is a critical activity whose start cannot be delayed without delaying the whole project.
\[ \boxed{\text{Option (D)}} \]