P of Durations Comp. Comp Later Mean Std Dev P of P of Activity Optimistic Pesim

Question

P of Durations Comp. Comp Later Mean Std Dev P of P of Activity Optimistic Pesimistic Durations Likely Comp. Bef. Comp. Later 50.00% 93.48% 4.19% Bef 194 50.00% 180 6.52% 210 95.81% 175 2.25% 120 90.00 18 15.00 6 5.00 33 20.00 24 21.00 30 25.00 22 14.00 32 21.33 50 30.00 5.00 194.00 7.33 53.78 1.00 0.33 3.00 1.00 2.33 2.00 1.33 4.67 21.78 3.67 13.44 9.26 85.67 76 1.00 0.11 9.00 1.00 5.44 4.00 1.78 12 975% 215.5 215.5 15 21 26 16 10 24 18 27 43 38 60 4 Observe the spreadsheet, calculate Probability of completing the project in less then 200 days and later than 200 days Explain why the sum of two calculations is 1 or 100%

Explanation / Answer

Given are the following data :

Mean duration of the project = m = 194

Standard deviation of duration of the project = Sd = 9.26

Let the Z value corresponding to the probability that the project can get completed in less than 200 days = Z1

Therefore,

M + Z1.Sd = 200

Or, 194 + 9.26.Z1 = 200

Or, 9.26.Z1 = 200 – 194 = 6

Or, Z1 = 6/9.26 = 0.648 ( 0.65 rounded to 2 decimal places )

Corresponding probability for Z1 = 0.65 using standard normal table = 0.74215

Therefore , probability of completing the project in less than 200 days = 0.74215

Hence, Probability of completing the project in more than 200 days = 1 – 0.74215 =0.25785

There are only two options when a project can get competed :

Since these two options together constitute an exhaustive set, Sum of probabilities of these two events should be 1 .

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