4). Eight maintenance activities, their normal durations in weeks, and the crew sizes for the normal condition are as follows:

Activity	Duration in Weeks	Crew size
AC	6	8
BC	6	7
BE	2	6
CD	3	2
CE	4	1
DF	7	4
EF	4	6
FG	5	10

3. Extra crew members can be used to expedite activities BC, CE, DF, and EF at a cost given below:

Extra Crew	Weeks Saved	Crash cost per week
1	1	$100
2	2	$120
3	2	$200
4	3	$250

If there is a penalty cost of $1,250 per week beyond the minimum maintenance time of 20 weeks, recommend the minimum cost schedule.

4. (Independent of part c) The table below, based on historical completion times, gives three estimates for each activity completion time. Determine the mean and variance of the expected project completion time and calculate the probability that the project is completed within the 20-week minimum maintenance time.

Activity	Optimistic	Most Likely	Pessimistic
AC	5	6	8
BC	4	6	10
BE	2	2	2
CD	2	3	7
CE	2	4	9
DF	5	7	13
EF	3	4	6
FG	4	5	16