Question

Dave Fletcher was able to determine the activity times for constructing his laser scanning machine. Fletcher would like to determine​ ES, EF,​ LS, LF, and slack for each activity. The total project completion time and the critical path should also be determined. Here are the activity​ times:

Activity   Time (weeks)   Immediate Predecessor(s)   Activity   Time (weeks)   Immediate Predecessor(s)
A 6 - E 3 B
B 7 - F 7 B
C 2 A G 9 C, E
D 1 A    H 6 D , F

Dave's earliest start​ (ES) and earliest finish​ (EF) are:

Activity ES EF

A ? 6

What is ES?

Answer 1

step 1	find early start, and early finish from the start of the project for each activity
step 2	Find Maximum EF and keep it as the LF of last activities. Max of EF's is 20

Activity	Duration, D	Early start, ES=Max of early finish of preceding activities	Early finish, EF = ES + D	Late finish, LF= Min of LS of successor activities	Late start, LS= LF - D
A	6	0	6
B	7	0	7
C	2	6	8
D	1	6	7
E	3	7	10
F	7	7	14
G	9	10	19	20
H	6	14	20	20

step 3

calculate LS for each activity after calculating its EF

Activity	Duration, D	Early start, ES=Max of early finish of preceding activities	Early finish, EF = ES + D	Late finish, LF= Min of LS of successor activities	Late start, LS= LF - D
A	6	0	6	9	3
B	7	0	7	7	0
C	2	6	8	11	9
D	1	6	7	14	13
E	3	7	10	11	8
F	7	7	14	14	7
G	9	10	19	20	11
H	6	14	20	20	14