PERT

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KaurP
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Posts: 94
Joined: Wed Apr 04, 2018 4:08 am

PERT

Postby KaurP Mon Aug 06, 2018 11:18 am

One of the questions with no explanation for the answer-

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, what is the duration uncertainty of the entire path?
o 21 days
o 30 days. Marked as correct Answer
o 42 days
o No statement is possible from the information given.

Can you please help me solve this?

Thanks!
manishpn
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Posts: 2577
Joined: Sat Jan 04, 2014 3:55 pm

Re: PERT

Postby manishpn Tue Aug 07, 2018 5:55 pm

This question from Oliver is quiet controversial, I am not an expert in statistics but us has been debated a lot.
Since almost all Math questions in exam are nowadays very simple you should not spend a lot of time on such questions

Data given is P = O for Activity 1 is 18 & Activity 2 is 24.
lets calculate P - O for project.

If we take information as per Rita, duration of uncertainity (P -O) is already provided for activities, so just adding up the two durations would give total duration of uncertainity for entire path.

Duration uncertainity of entire path = duration uncertainity of activity 1 + duration uncertainity of activity 2 = 18+24 = 42

however if we go with other approach

1. Calculate standard deviation of activities; SD = (P - O) / 6

2. Calculate variance of activities; variance = SD²

3. Calculate Total variance

4. Calculate Uncertainity; U = P-O

Activity A and Bs uncertianity is 18 and 24 respectively

SD of A = 18/6 = 3. of B = 24/6 = 4
Variance of A = 9 and of B =16
total variance = 20

Total variance = total SD²
0r 25= SD²
0r total SD = 5
total U = SD*6 =30







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Manish P
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