Question

What is the minimum cost of crashing the following project that Roger Solano manages at Slippery Rock University by 4 days? $______________

Activity	Normal Time (days)	Crash Time (days)	Normal Cost	Total Cost with Crashing	Immediate Predecessor(s)
A	6	5	$800	$1,100	-
B	8	6	$300	$400	-
C	6	5	$600	$650	-
D	6	3	$750	$1,500	A
E	5	3	$1,200	$1,650	C

	a.	$ 3550
	b.	$ 1550
	c.	$ 3800
	d.	$ 2500

Answer 1

Paths from start to end of project network is as follows:

Path	Duration
A-D	6 + 6 = 12 days
B	8 days
C-E	6 + 5 =11 days

Critical Path: A-D and project duration is 12 days.

Crashing principle: Crash only critical activities and prefer to crash the activity with lowest crashing cost per day.

The crashing cost per day is calculated is as follows:

Activity	Normal Time (days)	Crash Time (days)	Normal Cost	Total Cost with Crashing	Immediate Predecessor(s)	Allowable Crashing	Crashing Cost	Crashing cost per day
A	6	5	$800	$1,100	-	1	$300	300
B	8	6	$300	$400	-	2	$100	50
C	6	5	$600	$650	-	1	$50	50
D	6	3	$750	$1,500	A	3	$750	250
E	5	3	$1,200	$1,650	C	2	$450	225

A-D is critical path, and lowest cras

The crashing schedule is as shown below:

Crashing Sequence	0	1	2	3	4
Critical Paths	A-D	A-D	A-D C-E	A-D C-E	A-D C-E
Lowest crashing cost per week activity (crashing cost)		D ($250/ DAY)	D ($250/ DAY) C ($50/ DAY)	D ($250/ DAY) E ($225/ DAY)	A ($300/ DAY) E ($225/ DAY)
Activity Crashed	None	D	D, C	D, E	A, E
Crashing Duration	0	1	1	1	1
Project duration	12	11	10	9	8
A-D	12	11	10	9	8
B	8	8	8	8	8
C- E	11	11	10	9	8
Crash cost	$0	$250	$300	$475	$525
Cum. Crash cost	$0	$250	$550	$1025	$1550

Thus, to crash the project duration by 4 DAYS, the minimum additional cost required = $1550