What is the value of the view factor for two inclined flat plates having common edge of equal width, and with an angle of $$20$$ degrees?

A project consists of three parallel paths with mean durations and variances of $$(10,4), (12,4)$$ and $$(12,9)$$ respectively. According to the standard $$PERT$$ assumptions, the distribution of the project duration is

The precedence relations and durations of jobs in a project are given below:
(a) Draw the activity-on-arc project network
(b) Determine all critical path(s) and their duration(s).
(c) What is the total float for jobs $$B$$ and $$D?$$

Arrivals at a telephone booth are considered to be Poisson, with an average time of $$10$$ minutes between successive arrivals. The length of a phone call is distributed exponentially with mean $$3$$ minutes. The probability that an arrival does not have to wait before service is