Argh , still confused on Q9 of 2012 Ex 1 Networks.
Time Activity Person0-3 A John
3-10 D Lisa can start D when A finishes.
0-6 B Ken can start B at 0.
He cannot start C until he finishes B at 6
Lisa cannot start E until she finishes D at 10
6-10 C Ken has finished B and can start C at 6
10-16 E Lisa has finished D and can start E at 10
10 -15 F John can start F when Ken finishes C at 10
G can be done by anyone available when C finishes at 10. Lisa is busy with D and John is busy with F. So Ken can do G finishing at 17.
H can be done by anybody available when all of D, E and F have finished. Of these three, the last to finish is E at 16 and John or Lisa are available. Then H can finish at 21.
So, earliest finish of the entire project is 21 (D)