$($b$)$ What is the expected completion time $($in hours$)$ of this project?

$hr$

$($c$)$ What is the probability that the project can be completed within thirteen hours? $($Round your answer to four decimal places.$)$You may need to use the appropriate technology to answer this question.

A project consists of five activities as shown in the following table.

Naturally, the paint mixing precedes the painting activities. Also, both ceiling painting and floor sanding must be done prior to floor buffing.

$($a$)$ Construct the PERT$/$CPM network for this problem.