Probability of Project Completion

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The formula for activity variance is:

s$2=[($b $$ a$)/6]2,$ where b is the most pessimistic time and a is the most optimistic

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The formula for project variance is:

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Suppose our critical path had four activities with the following variances:

Activity A: $1\mathrm{.}78$

Activity B: $4\mathrm{.}00$

Activity C: $0\mathrm{.}69$

Activity D: $1\mathrm{.}00$

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What is the Project variance?

What is the Project Standard Deviation?

Suppose our project has a critical path of $16$ days. What is the probability that the project will finish by day $18?$

How many extra days do we need to generate a $99\%$ chance of finishing on time?