The time estimates obtained from four contractors P, Q, R and S for executing a particular job are as under:

Contractor Optimistic time (t₀) Most likely time (t₁) Pessimistic time (t_p)

P 5 10 13

Q 6 9 12

R 5 10 14

S 4 10 13

Which one of the contractors is more certain about completing the work in time:

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This question was previously asked in

JKSSB JE (Civil) Official Paper (Held On: 19 Nov, 2023)

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Answer 1

Concept:

To determine which contractor is more certain, we calculate the standard deviation (σ) for each contractor using the PERT formula:

\(\sigma=\frac{t_p-t_0}{6}\)

where σ is standard deviation, t_p is pessimestic time, and t₀ is optimistic time.

The smaller the standard deviation, the more certain the estimate is.

Calculation:

Contractor P: \(\sigma_P=\frac{13-5}{6}=1.33\)

Contractor Q: \(\sigma_R=\frac{12-6}{6}=1.00\)

Contractor R: \(\sigma_R=\frac{14-5}{6}=1.50\)

Contractor S: \(\sigma_S=\frac{13-4}{6}=1.50\)

Contractor Q is most certain about completing the job on time.