What is the likelihood of this project being completed earlier than 20 days?What is the completion time at 99.7 % confidence level?

Consider the following table:
ACTIVITY PREC. ACT. TIME ESTIMATES (days)
to tml tp te
A — 6 6 6
B A 4 5 6
C A 2 4 6
D B 4 6 8
E C 2 4 6
F D 1 5 3
1) Construct a PERT network.
2) By using ES, EF, LF, LS, find the slack of each activity and the critical path.
3) Find the completion time and the standard deviation (σ) for the project— round off the standard deviation to the nearest hundredth: two decimal places.
4) What is the completion time at 99.7 % confidence level?
5) What is the likelihood of this project being completed earlier than 20 days?
6) Between 19 and 22 days?

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