PERT Estimating

5 minutes 5 Questions

The Program Evaluation and Review Technique (PERT) is a statistical tool used in project management to represent tasks or activities and their relationships. A PERT estimate is calculated as (Optimistic + (4 X Most Likely) + Pessimistic) / 6. This technique is useful when activities do not follow the normal distribution and where impressionistic estimates are risky.

Guide to PERT Estimating

PERT Estimating is a crucial tool for determining accurate project schedules and resource allocation. PERT, or Project Evaluation and Review Technique, takes uncertainty into account and provides a range of possible task durations rather than a single, fixed timeline.

Importance: It helps in the identification of minimum time needed to complete a project, and the critical path or tasks that directly affect the project timeline. This helps in better planning, managing risks and efficient resource allocation.

Working: PERT uses 3 time estimates for each project activity: Optimistic (O), Pessimistic (P), and Most Likely (M). The estimated time for each task is calculated using the formula: (O + 4M + P) / 6.

Answering PERT Questions in Exam: To excel in exam questions related to PERT, keep the following points in mind:

- Understand the basic PERT concept, formula and its application
- Practice questions to reinforce your understanding and speed
- When interpreting a PERT chart, focus on the critical path
- Familiarize yourself with common time and resource allocation scenarios
- Work on estimation accuracy rather than precision

Remember each activity’s duration is estimated separately and independent of other tasks, and the calculated time is an estimate, not a precise value.

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Exam (Timed)

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Question 1

You're managing a project with an optimistic time of 10 days, a pessimistic time of 20 days, and a most likely time of 15 days. How will you calculate the PERT estimate?

18 days 13.5 days 15 days 16 days

Correct Answer: 15 days

To calculate the PERT (Program Evaluation and Review Technique) estimate, we use a weighted average of the optimistic, pessimistic, and most likely time estimates. The formula for the PERT estimate is:
PERT Estimate = (Optimistic + 4 × Most Likely + Pessimistic) ÷ 6
Given:

Optimistic time (O): 10 days
Pessimistic time (P): 20 days
Most likely time (M): 15 days

Let's calculate the PERT estimate:
PERT Estimate = (O + 4M + P) ÷ 6
= (10 + 4 × 15 + 20) ÷ 6
= (10 + 60 + 20) ÷ 6
= 90 ÷ 6
= 15 days

Therefore, the PERT estimate for the project is 15 days. This estimate takes into account the optimistic, pessimistic, and most likely time estimates, giving more weight to the most likely estimate (4 times as much as the optimistic and pessimistic estimates).

Question 2

You're leading a marketing campaign project. The optimistic time estimate is 4 weeks, pessimistic is 10 weeks and the most likely time is 5 weeks. What should be the PERT estimate?

6 weeks 5 weeks 5.67 weeks 7 weeks

Correct Answer: 5.67 weeks

The PERT (Program Evaluation and Review Technique) estimate is calculated using the following formula: PERT estimate = (optimistic time + 4 * most likely time + pessimistic time) / 6. So, substituting in the actual figures given, (4 weeks + 4*5 weeks + 10 weeks) / 6 equals to 5.67 weeks. Hence, the PERT estimate would be 5.67 weeks. All other answers are incorrect as they do not accurately follow the formula for PERT estimation.

Question 3

You are the project manager for a construction project. The optimistic time is 12 weeks, the pessimistic time is 20 weeks, and the most likely time is 16 weeks. What is the PERT estimate for this project?

17.5 weeks 15 weeks 16.33 weeks 18 weeks

Correct Answer: 16.33 weeks

The PERT Estimate calculation is given by (Optimistic Time + 4(Most Likely Time) + Pessimistic Time) / 6. In this scenario, the Optimistic Time is 12 weeks, the Most Likely Time is 16 weeks, and the Pessimistic Time is 20 weeks. So, the calculation would be (12 weeks + 4(16 weeks) + 20 weeks) / 6. The result is 16.33 weeks. So, the correct answer is 16.33 weeks. The other answers are incorrect because they are not the result of the PERT Estimate calculation for the given Optimistic, Most Likely, and Pessimistic times.

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