Module 5 CEE 473

What is duration?

Estimated time required to complete an activity — from start to finish.

What is activity duration directly related to?

Assigned resources and estimated work required.

What is the ideal length of an activity duration?

As short as possible, while balancing durations that are too short or too long.

When should long activities be broken into shorter activities?

When logical breaks can be identified.

How long should near-term activity durations be?

No longer than the reporting period.

What is the ideal activity duration for weekly reporting?

One working week or less.

Why should very short activity durations be avoided?

They require more frequent schedule updates.

What is a resource?

Anything required to perform work.

What are the two types of resources?

Labor and nonlabor.

What are examples of nonlabor resources?

Subcontracts, materials, machines, and equipment.

Why are resources assigned to activities?

To ensure activity durations are realistic and rational.

What are two important factors in accurate cost estimates?

Quantity takeoff accuracy and proper unit costs/production rates.

What information is important when using historical data?

Productivity rates.

How are activity durations generally recorded?

Whole days; always round up.

What is the formula for activity duration?

Duration = Total worker-hours / (Number of workers × Hours per day).

Excavation: $950 budget, $33.20/hr, 1 worker. Duration?

950 / (33.20 × 1 × 8) = 3.58 → 4 days.

Excavation: $950 budget, $33.20/hr, 2 workers. Duration?

950 / (33.20 × 2 × 8) = 1.79 → 2 days.

Formwork: 47 m² at 1.8 hr/m², 2 workers. Duration?

(47 × 1.8) / (2 × 8) = 5.29 → 6 days.

Formwork: 47 m² at 1.8 hr/m², 4 workers. Duration?

(47 × 1.8) / (4 × 8) = 2.64 → 3 days.

What information is needed for probability-based duration estimates?

Mean and standard deviation.

What is the formula for the Z-score?

Z = (X − Mean) / Standard Deviation.

What is the formula for duration at a given confidence level?

X = Mean + (Z × Standard Deviation).

What is the Z-score for 95% confidence (not exceeded)?

1.645.

What is the Z-score for 98% confidence (not exceeded)?

2.054.

Mean = 20 days, SD = 5 days. Duration for 95% confidence?

20 + (1.645 × 5) = 28.23 → 29 days.

Mean = 20 days, SD = 5 days. Duration for 98% confidence?

20 + (2.054 × 5) = 30.27 → 31 days.

Mean = 8 days, SD = 2.4 days. Duration for 95% confidence?

8 + (1.645 × 2.4) = 11.95 → 12 days.

Mean = 8 days, SD = 2.4 days. Probability of exceeding 10 days?

Z = (10 − 8) / 2.4 = 0.833. Probability ≈ 20.2%.

How do you calculate the probability a duration will be exceeded?

100% − Probability of not exceeding that duration.

What does "duration will not be exceeded" mean?

Find the probability to the left of the duration on the normal curve.

What does "duration will actually exceed" mean?

Find the probability to the right of the duration on the normal curve.