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# TOPIC: Does any one have any idea how to approach this PERT question?

## Does any one have any idea how to approach this PERT question? 4 years 1 month ago #22623

 Ali MOMENZADEHPISHROO Topic Author Offline User is blocked Posts: 10 Thank you received: 0 Together with your team, you applied three-point estimation on a critical path which consists of two activities. The following duration uncertainties are all calculated assuming a ±3sigma confidence interval. The duration uncertainty—defined as pessimistic minus optimistic estimate—of the first activity is 18 days; the second estimate has an uncertainty of 24 days. Applying the PERT formula for paths (beta distribution), what is the duration uncertainty of the entire path? o 21 days o 30 days o 42 days o No statement is possible from the information given FROM OLIVER LEMANN FREE SAMPLES Your e-mail address will never be displayed on the site. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable. Last edit: by Ali MOMENZADEHPISHROO.

## Does any one have any idea how to approach this PERT question? 4 years 1 month ago #22632

 Gabriella Dellino, PMP Offline Gold Boarder Posts: 266 Karma: 24 Thank you received: 93 Wow, Ali! That truly is a tough one! Let me recap the assumptions here: 1. Two activities on the critical path 2. Activity duration following a Beta distribution 3. Duration uncertainty (i.e., standard deviation, sigma) known for each activity. Please notice that the description here sounds a bit misleading to me. In fact, if you assume a beta distribution, the standard deviation is sigma = (P - O)/6, where P and O are the most pessimistic and most optimistic durations, respectively. Not that we will use this formula to solve this problem, but reading it as P - O confused me in the beginning. 4. Confidence interval as +/- 3sigma. This won't be needed to solve our problem Now, from some statistical theorems, we know that the variance of the project is equal to the sum of the variances of the activities on the critical path. In our case: var_p = var_1 + var_2 = (sigma_1)^2 + (sigma_2)^2 = 18^2 + 24^2 = 900 So the standard deviation for the project (i.e., its duration uncertainty) is sigma_p = sqrt(var_p) = 30. Therefore the correct answer should be option B. That said, I've never seen anything like this in the actual exam, nor even in the exam simulations I practiced. Thanks for sharing it. Gabriella Gabriella Dellino, PhD, PMP PMPrepCast Community Moderator Your e-mail address will never be displayed on the site. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.

## Does any one have any idea how to approach this PERT question? 4 years 1 month ago #22649

 Ali MOMENZADEHPISHROO Topic Author Offline User is blocked Posts: 10 Thank you received: 0 Awesome !Good job Thanks very much Gabriella Your e-mail address will never be displayed on the site. Check this box to be notified of replies to this topic. Note: BBcode and smileys are still usable.
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