Page 405 -

PROJECT SCHEDULING WITH UNCERTAIN ACTIVITY TIMES 385

Figure 9.11 Activity Time Distribution for Product Design (Activity A) for the Porta-Vac
Project

Most probable Expected (t)

Pessimistic
Optimistic

0 4 5 6 12
Activity Time (in Weeks)

When uncertain activity The Critical Path
times are used, the
critical path calculations When we have the project network and the expected activity times, we are ready to
will determine only the proceed with the critical path calculations necessary to determine the expected time
expected or average time required to complete the project and determine the activity schedule. In these
to complete the project.
The actual time required calculations, we treat the expected activity times (Table 9.5) as the fixed length or
to complete the project known duration of each activity. As a result, we can use the critical path procedure
may differ. However, for introduced in Section 9.1 to find the critical path for the Porta-Vac project. After the
planning purposes, the critical activities and the expected time to complete the project have been deter-
expected time should be
valuable information for mined, we analyze the effect of the activity time variability.
the project manager. Proceeding with a forward pass through the network shown in Figure 9.10, we can
establish the earliest start (ES) and earliest finish (EF) times for each activity. Next,
Activities that have larger
variances show a greater we make a backward pass through the network. The backward pass provides the
degree of uncertainty. latest start (LS) and latest finish (LF) times shown in Figure 9.12. The project is now
The project manager expected to take 17 weeks to complete.
should monitor the
progress of any activity
with a large variance
even if the expected time Table 9.5 Expected Times and Variances for the Porta-Vac Project Activities
does not identify the
activity as a critical Activity Expected Time (weeks) Variance
activity.
A 6 1.78
B 2 0.44
C 3 0.11
D 5 1.78
E 3 0.11
F 2 0.03
G 3 0.25
H 4 0.69
I 2 0.03
J 2 0.11
Total 32

Copyright 2014 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has
deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.