Question

The table below shows the output from a system that uses PERT for project scheduling. The project involves 12 interdependent activities and all times are reported in weeks. Based on the information provided, answer the following questions: IMMEDIATE EXPECTED ACTIVITY PREDECESSORS TIME EARLIEST EARLIEST LATEST LATEST START FINISH START FINISH 16 BNS lolos 12 4 31 28 43 32 10 6 38 D, J, K (a) What is the minimum expected time required to complete the project? (b) How is the expected project completion time affected if it takes 12 weeks (instead of the expected 8 weeks) to perform activity B? Why? (e) How is the expected project completion time affected if the start of activity H is delayed by one week? Why? (d) How is the expected project completion time affected if activity J takes 6 weeks (instead of 10 weeks)? Why?

Answer 1

a)Min expected time required to complete project=max value of latest finish time - min value of earliest start time=61-0=61

Hence it will take 61 weeks to complete project.

b)Here slack time for B is 8.Any activity with a slack/float time of zero is critical.Here B is not critical.Hence project time will not change.

c)Here H is critical activity as slack time is 0.Project duration will increase by 1 week.

d)Activity J is critical as slack time is 0.Project duration will be reduced and can be recalculated as follows:

As J is predecessor of L,we calculate early start

ES(L)=max[ES(D)+T(D),ES(J)+T(J),ES(K)+T(K)]

=max[10+6,43+6,32+6]

=49

Now completion time for project will be ES(L)+T(L)

=49+8=57

Hence project will be completed early by 61-57=4 weeks.

[Note ES is Earliest start time T is expected time]