Question: how to calculate the variance of the critical path?
Answer: Project duration expected E = 5 + 15 + 4 + 5 = 29 days (i.e. the total of te-s for activities on the Critical Path).
Variance of the Critical Path = 2.79 + 2.79 + 0.45 + 0 = 6.03.
Standard Deviation (SD) of project duration is √6.03 = 2.46.