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D1 edexcel help please!

Hi guys,

I am just going through the textbook and I am so confused over a scheduling diagram question! Please can somebody explain Example 14 (in chapter 5) to me? I don't understand how you know to extend the minimum time, nor why the critical path is not on the top row? I don't think the book explains it very well lol...

Thanks in advance :smile:
Original post by Zippyzazu
Hi guys,

I am just going through the textbook and I am so confused over a scheduling diagram question! Please can somebody explain Example 14 (in chapter 5) to me? I don't understand how you know to extend the minimum time, nor why the critical path is not on the top row? I don't think the book explains it very well lol...

Thanks in advance :smile:


Heya, I'm going to put this in the Maths forum for you as you should get more responses there.

You should also check out the forum to see if there's any other threads there which might be helpful to you!

http://www.thestudentroom.co.uk/forumdisplay.php?f=38
Original post by Zippyzazu
Hi guys,

I am just going through the textbook and I am so confused over a scheduling diagram question! Please can somebody explain Example 14 (in chapter 5) to me? I don't understand how you know to extend the minimum time, nor why the critical path is not on the top row? I don't think the book explains it very well lol...

Thanks in advance :smile:


I wish I had the textbook on me. If you don't get any replies and are willing to post the example I could try to help. :smile:
you really need to post the question for us :redface:
Original post by Zippyzazu
Hi guys,

I am just going through the textbook and I am so confused over a scheduling diagram question! Please can somebody explain Example 14 (in chapter 5) to me? I don't understand how you know to extend the minimum time, nor why the critical path is not on the top row? I don't think the book explains it very well lol...

Thanks in advance :smile:


I haven't got the book but I can guess your problem. There are two sorts of scheduling puzzles. If there is a fixed number of workers which is smaller than the number you would need to complete the project in the minimum time, you must not give all of the critical activities toone worker, but must go through all of the activities one at a time, allocating them to a worker.

If there are as many workers as you like, that's when the project can be finished in the minimum time and so might as well give all of the critical activities to one worker
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Original post by tiny hobbit
I haven't got the book but I can guess your problem. There are two sorts of scheduling puzzles. If there is a fixed number of workers which is smaller than the number you would need to complete the project in the minimum time, you must not give all of the critical activities toone worker, but must go through all of the activities one at a time, allocating them to a worker.

If there are as many workers as you like, that's when the project can be finished in the minimum time and so might as well give all of the critical activities to one worker


Original post by the bear
you really need to post the question for us :redface:


Original post by SeanFM
I wish I had the textbook on me. If you don't get any replies and are willing to post the example I could try to help. :smile:



Sure thing, I don't have the textbook either so I've had to use the online one.. Here's an image of the example though! Thanks in advance :smile: (sorry the image is in two parts as one document was too large to upload)
d1 question.docx280.8KB
d1 question part 2.docx271.1KB
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Original post by tiny hobbit
I haven't got the book but I can guess your problem. There are two sorts of scheduling puzzles. If there is a fixed number of workers which is smaller than the number you would need to complete the project in the minimum time, you must not give all of the critical activities toone worker, but must go through all of the activities one at a time, allocating them to a worker.

If there are as many workers as you like, that's when the project can be finished in the minimum time and so might as well give all of the critical activities to one worker


Yep that's pretty much what it is.. It probably sounds silly but how do you know which worker to give each task to? :dontknow: Thank you! :colondollar:
Original post by Zippyzazu
Yep that's pretty much what it is.. It probably sounds silly but how do you know which worker to give each task to? :dontknow: Thank you! :colondollar:


The best guidelines is to work out the "latest start time" for each activity, i.e. largest time at the finish of the activity - duration. Then get the activities with the smallest "latest start time" going as soon as you can (once the activities before them are finished). When any worker finishes an activity, give them another one, based on the numbers I've given above.
Original post by Zippyzazu
Yep that's pretty much what it is.. It probably sounds silly but how do you know which worker to give each task to? :dontknow: Thank you! :colondollar:


From the example it looks like when a worker is free you look at all the events that can be done and choose the one with the earliest latest finish time (Hence the 17<21 in the 'explanation' when the worker chooses between C and D). If they're the same (as in later on for G,I,H) just choose them in a sensible order and minimise the time).
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Original post by tiny hobbit
The best guidelines is to work out the "latest start time" for each activity, i.e. largest time at the finish of the activity - duration. Then get the activities with the smallest "latest start time" going as soon as you can (once the activities before them are finished). When any worker finishes an activity, give them another one, based on the numbers I've given above.


Original post by SeanFM
From the example it looks like when a worker is free you look at all the events that can be done and choose the one with the earliest latest finish time (Hence the 17<21 in the 'explanation' when the worker chooses between C and D). If they're the same (as in later on for G,I,H) just choose them in a sensible order and minimise the time).


Ohh I think I've got it! Thank you :smile:
I just thought it was a bit random to be honest, the textbook only has one question on it and I haven't (yet) come across it in any past papers...
:angry:
Original post by Zippyzazu
Ohh I think I've got it! Thank you :smile:
I just thought it was a bit random to be honest, the textbook only has one question on it and I haven't (yet) come across it in any past papers...


For a while from 2009, there were no questions on scheduling, so when they did ask it, people were surprised and started the usual "I haven't seen that before" conversation.
Original post by Zippyzazu
Ohh I think I've got it! Thank you :smile:
I just thought it was a bit random to be honest, the textbook only has one question on it and I haven't (yet) come across it in any past papers...


Best to be prepared for anything though :wink:. Especially with all the weird stuff they did in last year's paper.
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Original post by SeanFM
Best to be prepared for anything though :wink:. Especially with all the weird stuff they did in last year's paper.


Haha that is true, hoping to do well enough in C3 and C4 so that D1 isn't too stressful :P But you never know lol... I haven't seen last year's paper but my teacher's giving us a mock next week which may well be the one you're talking about :s-smilie:
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Original post by tiny hobbit
:angry:

For a while from 2009, there were no questions on scheduling, so when they did ask it, people were surprised and started the usual "I haven't seen that before" conversation.



Hmm okay... I guess I'll just have to wait and see :biggrin: scheduling isn't too bad, much better than linear programming in my opinion :P
Original post by Zippyzazu
Haha that is true, hoping to do well enough in C3 and C4 so that D1 isn't too stressful :P But you never know lol... I haven't seen last year's paper but my teacher's giving us a mock next week which may well be the one you're talking about :s-smilie:


Ah right, D1 will be handy for adding to your UMS :smile: good luck!
Original post by Zippyzazu
Haha that is true, hoping to do well enough in C3 and C4 so that D1 isn't too stressful :P But you never know lol... I haven't seen last year's paper but my teacher's giving us a mock next week which may well be the one you're talking about :s-smilie:


Make sure after your mock that your teacher gives you all of the recent papers, i.e. June 2014 normal and R and IAL and also January 2015 IAL. These papers were written by the new examiner, so give you some idea of his way of thinking.
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Original post by SeanFM
Ah right, D1 will be handy for adding to your UMS :smile: good luck!


Thank you! :smile:
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Original post by tiny hobbit
Make sure after your mock that your teacher gives you all of the recent papers, i.e. June 2014 normal and R and IAL and also January 2015 IAL. These papers were written by the new examiner, so give you some idea of his way of thinking.


Ahh okay, I will do! Are they significantly harder or just more wordy or..? Thanks :smile:
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Also just another random Q please everyone- you know the linear programming Qs where you have 'a blend' etc, could they ever ask us to work backwards from the graph so we'd have to realise it's a 'blend' or is it not that cruel? :P
Original post by Zippyzazu
Ahh okay, I will do! Are they significantly harder or just more wordy or..? Thanks :smile:


Just different enough to upset you in an exam. There's nothing that I can remember that is particularly hard and they probably wouldn't worry you if you were working through them in class.

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