![standard normal table to find the positive critical value standard normal table to find the positive critical value](https://cdn1.byjus.com/wp-content/uploads/2020/11/Z-Score-Table-1.png)
With the above t e -s and the activities with the precedent relationship of events we would like to prepare the network construction and then we find:ġ. To Calculate the Estimated time t e per activity as per PERT: (d) Find the estimated weeks of completion with a probability of 90%. (c) Find the probability of completing the project in 32 weeks (b) Identify the critical path on the network Illustration 3: (on Probability as per PERT):įollowing is a table of activities of a project with estimated optimistic, most likely and pessimistic duration in weeks:Ĭonsidering the above details, we are to: We know T E of 36 days as probability 0.5., T s of 41 days being greater than T E, we are to add 0.3413 with 0.5 and find probability of 41 days as 0.50 + 0.34 = 0.84 or 84%. The normal distribution table shows the value for 1 as 0-3413. SD = √Total Variance of all critical activitiesĭeviation of the schedule date, T s (which is given as 41 days) in units of SD is Z and Standard deviation of the project duration (make image) (b) Variance of the activities S, 2 on the Critical Path Total of variances of Critical Path = 25. (a) Standard deviation of the activities duration, S t =t p-t o/6 (3) The Critical Path represents activities A, C, G and I. Legends (2) The critical path shown with double-line arrows joining the events showing EST = LFT. Network construction with t e-s and the critical path. Step 1: Calculate the estimated time t per activity as per PERT: (d) Find the probability of completing the project (following the critical path) in 41 days. We have already worked out Ts and SD of the illustrated projected detailed on the table.įollowing the PERT we can answer questions like: When we would like to find the probability of a target scheduled date Ts, PERT works out the T E and SD as explained already and then finds out how much T s is deviated from the mean distribution (T E) in units of standard deviation (SD). When we say the project duration expected as T E we consider T E as the mean of the distribution with probability of 0-5.įrom the above calculated details, PERT suggests to work out the deviations from the mean of the distribution in units of standard deviation and read the probability from the normal distribution table. This is valid even when we accumulate the t e-s of all preceding events and can still say the probability as 0.5 for the cumulative time as on that event. We have seen earlier that t has the probability of 0-5 and this probability is applicable even on a cumulative situation till we reach the end event.