Standard Deviation Calculation
Started by Veena Mehra, Jan 14 2014 06:48 AM
1 reply to this topic
#1Posted 14 January 2014  06:48 AM
A project manager made 3point estimates on a critical path and found the following results:
Need help is calculating the below problem, found in one of the mock test. Pls. help Optimistic Most Likely Pessimistic PERT Weighted Avg Act. A 12 15 24 16 Act B 8 9 14 9.7 Act. C 15 19 27 19.7 Act. D 10 14 28 15.7 Act. E 17 20 35 22 estimate for the critical path: 83.1 Assuming ±3 sigma precision level for each estimate, what is the standard deviation of the allover path? 1. App. 4.2 days 2. App. 5.2 days 3. App. 6.2 days 4. You can not derive the path standard deviation from the information given. #2Posted 24 March 2014  03:33 AM
Standard deviation of allover path is the square root of its variance. Variance of allover path is the sum of variances of each individual activity. Activity variance is equal to its squared standard deviation. Standard deviation of a 3point PERT estimate is (PO)/6. Thus, StDev( A ) = (2412)/6 = 2 ; Var( A ) = 4 StDev( B ) = (148)/6 = 1 ; Var( B ) = 1 StDev( C ) = (2715)/6 = 2 ; Var( C ) = 4 StDev( D ) = (2810)/6 = 3 ; Var( D ) = 9 StDev( E ) = (3517)/6 = 3 ; Var( E ) = 9 Var( Path ) = Var( A ) + Var( B ) + Var( C ) + Var( D ) + Var( E ) = 4+1+4+9+9 = 27 StDev( Path ) = SQRT(27) = 5.2 Correct answer is 2. Edited by killzeghost, 24 March 2014  03:34 AM. 0 user(s) are reading this topic0 members, 0 guests, 0 anonymous users 

