Question

PM.62 The US government has recently contracted with Boeing to build its fleet of airborne tankers. The project has been laid out with durations (in weeks), predecessors, and costs included:

Activity	Normal Time (weeks)	Crashed Time (weeks)	Normal Cost	Crashed Cost	Predecessor(s)
A	11	10	$1,500	$1,650	-
B	7	5	$1,200	$2,490	-
C	5	4	$900	$1,200	B
D	4	2	$2,100	$3,000	A
E	2	1	$550	$1,250	B
F	4	3	$660	$1,050	E
G	10	6	$560	$1,040	C, D, F

What is the critical path of the project?

		B-C-G
		A-D-G
		B-E-F-G

If you wanted to shorten the overall duration of the project, which activity would you crash first?

		B
		E
		C
		G

What would be the weekly crashing cost of the activity you selected in the previous question? (Display your answer to two decimal places.)

   

Crash the project by 5 weeks. What is the total cost of crashing the project (just the additional cost, not total project cost)? (Display your answer to two decimal places.)  

   

Answer 1

Critical path is longest path of the project = A-D-G = 25 weeks

We will crash activity G first as it is on critical path.

Weekly crashing cost = (1040-560) /(10-6) = $120 / week

Now to crash project by 5 weeks, we first crash G by 4 weeks. This shortens all paths by 4 weeks. Next we crash A by 1 week. The project duration now is 20 weeks. We Crash A as it has lower weekly crash cost compared to D.

Total additional cost = Crash cost - Normal cost = (1040-560) +(1650-1500) = $630