RCDD · Question #161
What is the PERT estimate of time for cable placement on a given job? - Optimistic time is 100 hours - Most likely time is 125 hours - Pessimistic time is 210 hours
The correct answer is C. 135 hours. The PERT formula calculates a weighted average of three time estimates, giving the most likely estimate four times the weight of the others.
Question
What is the PERT estimate of time for cable placement on a given job?
- Optimistic time is 100 hours
- Most likely time is 125 hours
- Pessimistic time is 210 hours
Options
- A100 hours
- B125 hours
- C135 hours
- D155 hours
- E175 hours
How the community answered
(43 responses)- A7% (3)
- B14% (6)
- C74% (32)
- D2% (1)
- E2% (1)
Why each option
The PERT formula calculates a weighted average of three time estimates, giving the most likely estimate four times the weight of the others.
100 hours is only the optimistic estimate and does not apply the PERT weighted average formula across all three time values.
125 hours is only the most likely estimate and ignores the pessimistic value entirely, which is not the PERT calculation.
The PERT formula is (Optimistic + 4 x Most Likely + Pessimistic) / 6. Substituting the given values: (100 + 4x125 + 210) / 6 = (100 + 500 + 210) / 6 = 810 / 6 = 135 hours. The fourfold weighting on the most likely estimate reflects its statistically higher probability of occurrence.
155 hours results from a simple unweighted arithmetic mean of the three values, which is not the PERT formula.
175 hours is not produced by the PERT formula under any standard interpretation of these three inputs.
Concept tested: PERT three-point weighted average time estimation
Source: https://www.pmi.org/learning/library/three-point-estimating-techniques-6683
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