Can someone explain networks question 9?

[chikka]

Word is that the answer was D.

[Will T]

To begin with, John and Ken start working on Tasks A and B respectively.
John finishes in 3 minutes, and now Task C and D are unlocked whilst Ken is halfway through task B.
Lisa will start working on task D for 3 minutes whilst Ken finishes B.
After this initial 6 minutes Ken will have finished B and now task E will be unlocked.
So, Lisa will begin task E and Ken will begin task C.
After 4 minutes, Ken will finish task C and unlock tasks F and G, meanwhile, Lisa will be 4 minutes into completing task E.
So at this point, the 10 minute mark, John will start working on task F whilst Ken works on task G.
2 minutes after this, Lisa will finish task E and resume working on task D (which had already been worked on for 3 minutes).
At this stage, the 12 minute mark, John have worked through 2 minutes of task F and have 3 minutes remaining, whilst Ken will have worked through 2 minutes of task G and have 5 minutes remaining. Now, in the next 3 minutes, John will complete task F, but that does not fully unlock task H, as Lisa will need to finish task D before (this is how you get answer C. 20 and this was my mistake).
Lisa will take 4 minutes to complete task D, and by this time John will have finished task F, and Ken will have 1 minute left of task G.
At this point, the 16 minute mark, task H and G need to be finished off. Lisa or John or Ken can do this last bit, but it will take 5 minutes no matter how they work.

Hence, 16 + 5 = 21. So it will take them 21 minutes and the answer will be D. (This was probably the hardest question on the exam).

[chikka]

yeh, had a look at it when I got home. Can't believe I missed that! Actually wanted to change my answer to D on impulse but decided against it. Oh well!

[shmootz]

To begin with, John and Ken start working on Tasks A and B respectively.
John finishes in 3 minutes, and now Task C and D are unlocked whilst Ken is halfway through task B.
Lisa will start working on task D for 3 minutes whilst Ken finishes B.
After this initial 6 minutes Ken will have finished B and now task E will be unlocked.
So, Lisa will begin task E and Ken will begin task C.
After 4 minutes, Ken will finish task C and unlock tasks F and G, meanwhile, Lisa will be 4 minutes into completing task E.
So at this point, the 10 minute mark, John will start working on task F whilst Ken works on task G.
2 minutes after this, Lisa will finish task E and resume working on task D (which had already been worked on for 3 minutes).
At this stage, the 12 minute mark, John have worked through 2 minutes of task F and have 3 minutes remaining, whilst Ken will have worked through 2 minutes of task G and have 5 minutes remaining. Now, in the next 3 minutes, John will complete task F, but that does not fully unlock task H, as Lisa will need to finish task D before (this is how you get answer C. 20 and this was my mistake).
Lisa will take 4 minutes to complete task D, and by this time John will have finished task F, and Ken will have 1 minute left of task G.
At this point, the 16 minute mark, task H and G need to be finished off. Lisa or John or Ken can do this last bit, but it will take 5 minutes no matter how they work.

Hence, 16 + 5 = 21. So it will take them 21 minutes and the answer will be D. (This was probably the hardest question on the exam).

Any chance of saying what you are trying to do in layman's terms? I just chose the critical path (knowing that was too easy to be right). If I know what you're trying to do I may have better luck understanding your solutions. Thank you!

[Will T]

To begin with, John and Ken start working on Tasks A and B respectively.
John finishes in 3 minutes, and now Task C and D are unlocked whilst Ken is halfway through task B.
Lisa will start working on task D for 3 minutes whilst Ken finishes B.
After this initial 6 minutes Ken will have finished B and now task E will be unlocked.
So, Lisa will begin task E and Ken will begin task C.
After 4 minutes, Ken will finish task C and unlock tasks F and G, meanwhile, Lisa will be 4 minutes into completing task E.
So at this point, the 10 minute mark, John will start working on task F whilst Ken works on task G.
2 minutes after this, Lisa will finish task E and resume working on task D (which had already been worked on for 3 minutes).
At this stage, the 12 minute mark, John have worked through 2 minutes of task F and have 3 minutes remaining, whilst Ken will have worked through 2 minutes of task G and have 5 minutes remaining. Now, in the next 3 minutes, John will complete task F, but that does not fully unlock task H, as Lisa will need to finish task D before (this is how you get answer C. 20 and this was my mistake).
Lisa will take 4 minutes to complete task D, and by this time John will have finished task F, and Ken will have 1 minute left of task G.
At this point, the 16 minute mark, task H and G need to be finished off. Lisa or John or Ken can do this last bit, but it will take 5 minutes no matter how they work.

Hence, 16 + 5 = 21. So it will take them 21 minutes and the answer will be D. (This was probably the hardest question on the exam).

Any chance of saying what you are trying to do in layman's terms? I just chose the critical path (knowing that was too easy to be right). If I know what you're trying to do I may have better luck understanding your solutions. Thank you!

Sorry for not being clear, the reason choosing the critical path is not correct is because there are going to be delays as only certain people can work on certain tasks at a time.
The first problem occurs at C, as after A is finished, there is going to be a 3 minute delay before Ken can start task C (because Ken is working on task B). And this goes on and on throughout the network. You just need to think about it a little bit.

[oneoneoneone]

I made a diagram to figure out when things can happen.

I attached it below.

[Tennisacean]

Thanks so much for the answers, and the explanation for Q5, i didnt know that u could get an euler curcuit from a complete graph, however i still got the answer correct by just counting the degree of vertices, so i unintentionally got the answer correct