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# Edexcel D1 Jan 23 2013 Revision thread watch

1. (Original post by otrivine)
can I ask for question 12) review exercise2 have they made a mistake on part e and f
I think so :/ my answer is nothing like the one in the back of the book and I didn't understand part f)...but then again I was too lazy to draw my own diagram so ended up using the one at the back of the book.
2. (Original post by WavingFLag)
Its May 2010 Q2 b
If you can tell me what its asking I would be eternally grateful

Is that: Complete Matrix 1 in your answer book, to represent the network.

If so, I have the answer booklet infront of me, and it shows a distance matrix (Like on page 48 of the textbook) and it has blank boxes that you have to fill in. Basically you just copy the number from the network shown.

It is very obvious if you have the answer booklet to write in, I assume you don't have that?
3. I can only visualise and do scheduling with a gantt chart but this will take too long. What is a good method for scheduling? (I did the june d1, with scheduling in it and messed that up...)
4. (Original post by lollage123)
I can only visualise and do scheduling with a gantt chart but this will take too long. What is a good method for scheduling? (I did the june d1, with scheduling in it and messed that up...)
I always write them all down at the side and then play around with them from there.

I always struggle with linear programming when you have to formulate your own constraints. Does anyone have any tips for that?
5. (Original post by Meme4)
Is that: Complete Matrix 1 in your answer book, to represent the network.

If so, I have the answer booklet infront of me, and it shows a distance matrix (Like on page 48 of the textbook) and it has blank boxes that you have to fill in. Basically you just copy the number from the network shown.

It is very obvious if you have the answer booklet to write in, I assume you don't have that?
OH!! by complete it means to put the numbers in? Yeah I can do that lol!
I just misunderstood the question

By the way I got 12 e and f. Shall I scan and upload?
F is basically asking - plug the x and y values back into the 3 constraints - 2x+3y=33 x+2y=20 and 7x+ 8y=112. And see if they're optimal.
So optimal values are x=6 and y=7
If you put that back in to 3 constraints you get
2x+3y which is 2x6 + 3x7 = 33. that is optimal
x+2y which is 6 + 2x7 = 20, again this is optimal
and then 7x+ 8y which is 7x6 + 8x7 = 98, and as the maximum is 112, then you're wasting 14 hours.
Make sense??
6. (Original post by WavingFLag)
You're right, they don't mention if it is minimum or maximum. Firstly its nothing to worry about as all past papers make clear if they're looking for optimal minimum or optimal maximum. In this case I would assume optimal to be maximum as they have given you a new objective line 'x+2y' and to find optimal generally means to find best/highest value to get best/highest result.

As far as I know you can list the edges in any order. I would normally go for alphabetical as that is how most/all mar schemes list them.

How is everyone feeling?
Okay cheers
7. Any ideas on what could come up, looking the past few papers? I'm really hoping scheduling/drawing an activity network doesn't come up!
8. Anyone know where I can get the june '12 mark scheme?! I can't get it anywhere! I'm honestly hoping no definitions or scheduling comes up!!!
9. (Original post by Satta101)
Anyone know where I can get the june '12 mark scheme?! I can't get it anywhere! I'm honestly hoping no definitions or scheduling comes up!!!
https://www.dropbox.com/sh/zjl5q8pn9...2012%20May.pdf
10. Cheers for the paper, would you happen to have the mark scheme aswell?
11. (Original post by FLLF)
Cheers for the paper, would you happen to have the mark scheme aswell?
Sorry wrong file linked before. Here you go.
https://www.dropbox.com/sh/zjl5q8pn9...k%20Scheme.pdf
12. (Original post by Mujahid11288)
Sorry wrong file linked before. Here you go.
https://www.dropbox.com/sh/zjl5q8pn9...ark Scheme.pdf
Thanks

Good luck tomorrow
13. I'm freaking out!!! Feel so much pressure on me to get these grades for university. So D1 needs to boost marks up so I can afford to drop more in C3. Aghhhhhh. Stressed. Any last minute tips?

Thanks a million.
14. On jan 2011 on the last part of question 3, why does it have to be kruskals rather than prims?
15. (Original post by brittanna)
On jan 2011 on the last part of question 3, why does it have to be kruskals rather than prims?
Yh thats weird I would have thought it would be prims too.
16. I thought same thing too since Prim's is the one you can choose starting vertex/edge, so why use Kruskal? But I'm thinking if you explain it surely you can get the marks.
17. (Original post by Mujahid11288)
Yh thats weird I would have thought it would be prims too.
Because in the examiners report, it said prims was the wrong answer but it didn't say why.
18. Guys, why in the markscheme, they put the values S, T and R in line 1? Also they put Yes in line 1?
Shouldn't it be put in separate lines?
Attached Images

19. (Original post by laurar0b)
I'm freaking out!!! Feel so much pressure on me to get these grades for university. So D1 needs to boost marks up so I can afford to drop more in C3. Aghhhhhh. Stressed. Any last minute tips?

Thanks a million.
Tips
1) When scheduling make sure you consider a) the lowest late event time in deciding which activity to do next and b) that the activity follows the activity before it. Eg don't put down d before c if d comes after c in activity network
2) When ordering for binary seach use quick sort rather than bubble
3) When trying to work out why you can't get complete matching look for 2 people who can only do the same job e.g a and b can only do activity 3. Or look for someone who does 2 jobs no one else can do, so that if they do one there is no one to do other e.g b can do 3 & 4 and no one else can do either.
4) When calculating late/early event time, remember early time has to be as high as it can be and late time has to be as low. Don't overlook dummies.

Final tip? Go to bed, for D1 you need to be sharp and well rested otherwise you'll make mistakes. Good luck all

By the way anyone know how to plot objective line? I do it by swapping x and y co-efficients. Any help would be appreciated.
20. (Original post by Putch1)
Guys, why in the markscheme, they put the values S, T and R in line 1? Also they put Yes in line 1?
Shouldn't it be put in separate lines?
We discussed this earlier and concluded that the way you lay out table doesn't matter as long as output is correct. Judging by how many lines you get you can work out when to move on to next line. Usually move onto next line when you go back to beginning of flow chart. But it honestly doesn't matter, don't worry about it.

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