Question

Activities, predecessors and duration for a School Building Project

Activity	Description	Immediate predecessor	Duration (days)
A	Clear Site and mobilize labour and equipment	None	5
B	Excavate foundation	A	15
C	Procure materials (sand, cement, chippings etc.)	A	10
D	Pour foundation concrete	B, C	5
E	Mould sandcrete blocks (substructure)	C	5
F	Construct substructure block work	D, E	15
G	Construct superstructure block work	F, H	30
H	Make doors and window frames	I	10
I	Procure and preserve roof timber	C	10
J	Roofing, plastering and painting	G, I	25
K	Fabricate roof trusses	I	15
L	Mould sandcrete blocks (superstructure)	C	10

1. Draw the network diagram.
2. What is the critical path of the above project?
3. Calculate the total and free floats for the activities.

Answer 1

For each non-critical activity, the total float, and free float calculations are shown in Table

Activity		Earliest time			Latest time	Earliest time	Latest time
(i,j)	Duration	Start			Finish	Finish	Start	Total Float	Free Float
	(tij)	(Ei)	(Ej)	(Li)	(Lj)	(Ei+tij)	(Lj-tij)	(Lj-tij)-Ei	(Ej-Ei)-tij
[1]	[2]	[3]	[4]	[5]	[6]	(7)=(3)+(2)	(8)=(6)-(2)	(9)=(8)-(3)	(10)=((4)-(3))-(2)
2-4	10	5	15	5	20	15	10	5	0
4-3	0	15	20	20	20	15	20	5	5
4-5	5	15	25	20	25	20	20	5	5
4-6	10	15	25	20	30	25	20	5	0
4-9	10	15	95	20	95	25	85	70	70
6-7	10	25	40	30	40	35	30	5	5
6-8	0	25	70	30	70	25	70	45	45
6-9	15	25	95	30	95	40	80	55	55

note that for critical activity all floats are 0.

critical path is shown in fig. activities along the critical path are the critical activites'

thank you