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# Edexcel D1 Jan 23 2013 Revision thread watch

1. (Original post by FLLF)
Cheers, I was wondering if you could clear one other thing up.

When using kruskals and you have to select arcs, what happens if they're both the same weight? Do you show them both in the same bracket to show they're considered at the same time?
Just add one of them and then add the other like you would normally in any order.
The book says: "If there is a choice of equal arcs, consider each in turn"

The bracket used in the mark scheme when one number is on top of the other just shows that they can be added in any order.
2. Found a nice link to one of the previous posts detailing the definitions:

http://www.thestudentroom.co.uk/atta...8&d=1262343874

not sure wheres its come from so cant credit it
3. I should be ok for this only thing that I find difficult are the second part of route inspection questions and if a flowchart questions comes up i'll be screwed as the book doesn't go through it properly and there are so few past paper questions.
4. a good thing about d1 is ive never taken more than 65 mins to complete a mock exam. Although with exam nerves it'll probably take 75 mins for me giving 15 mins to check over any silly mistakes.
5. (Original post by Kishan91)
Quick question When drawing an activity network, is the start event number a 0 or a 1 as in the textbook they always start at event number 0, but in the January 2009 paper mark scheme they started at 1.

Attachment 194848
Although that doesn't matter that much, I would say 0
6. (Original post by Ollie.loney)
Just a quick question. In flow chart style questions when should you begin a new row in the table. ?
Guys we can't just leave this one, this is the most active thread and nobody knows the answer. There is one question among every past paper, that is Q5 January 2010. It was 2 years ago so it might come up this year.

The question is:

Why do you leave gaps, after answering the questions but in the first row there is no gap. And also I understand how to find the purpose of the flow charts eg: to find HCF of a number or finding prime factors of a number. But in this question it is about taxes and I do not get how you would find it...
7. As far as I can tell how you fill the table doesn't matter, as long as you get the right ouput. Also sometimes its quite obvious when to move to next line. Like maybe you got a 'no' and have to go back to the top of flow chart so start a new line. Finding purpose of flow chart is a guessing game - try common one eg hcf, multiples, division, square root, sum of two numbers etc.

I have one question - when do you stop sorting using quick sort? Is it when you have chosen all as pivots or when the sub list is down to 1? I have seen this type of comment on a lot of past papers. Can anyone help? I'm a private student, so if anyone could ask a teacher and let me know that would be great.

Thanks
8. (Original post by WavingFLag)
As far as I can tell how you fill the table doesn't matter, as long as you get the right ouput. Also sometimes its quite obvious when to move to next line. Like maybe you got a 'no' and have to go back to the top of flow chart so start a new line. Finding purpose of flow chart is a guessing game - try common one eg hcf, multiples, division, square root, sum of two numbers etc.

I have one question - when do you stop sorting using quick sort? Is it when you have chosen all as pivots or when the sub list is down to 1? I have seen this type of comment on a lot of past papers. Can anyone help? I'm a private student, so if anyone could ask a teacher and let me know that would be great.

Thanks
yeah the guy on exam solutions put just one answer per line for the flowchart but the mark scheme had three things for the first line and then 1 on each of the remaining rows so I don't think it matters how you fill in the flowchart aslong as you get the right output. and I was always taught to keep quick sorting until you have made all the numbers pivots, but again I hope I wont get an examiner so pedantic to make me drop marks if I over pivot.
9. and also my teacher said they wont ask you to draw a precendence graph only ask you to explain why they used a dummy and/or do the earliest and latest start times. Do you guys think I should practice drawing the graphs or hope it doesn't come up?
10. (Original post by WavingFLag)
As far as I can tell how you fill the table doesn't matter, as long as you get the right ouput. Also sometimes its quite obvious when to move to next line. Like maybe you got a 'no' and have to go back to the top of flow chart so start a new line. Finding purpose of flow chart is a guessing game - try common one eg hcf, multiples, division, square root, sum of two numbers etc.

I have one question - when do you stop sorting using quick sort? Is it when you have chosen all as pivots or when the sub list is down to 1? I have seen this type of comment on a lot of past papers. Can anyone help? I'm a private student, so if anyone could ask a teacher and let me know that would be great.

Thanks
The way I do (i am sixth form student) is i circle each pivot when it is on place. It won't move to right or left once it is circled. Also when there is a number or letter in between two circles obviously you can just circle that aswell because it is in place.
Finish it once everything is circled.
Also in each row state your newly selected pivot (that is not moved yet) perhaps with a square and in next row convert it to a circle...
11. Thanks that's ace - can anyone confirm that with a teacher?
I think you should definitely practise drawing it. I've done a couple of past papers where they ask you to draw it.
Also I would advice everyone to do the review exercise questions in textbook. They're tougher than most exam questions so they really prepare you.
12. (Original post by I witness I)
yeah the guy on exam solutions put just one answer per line for the flowchart but the mark scheme had three things for the first line and then 1 on each of the remaining rows so I don't think it matters how you fill in the flowchart aslong as you get the right output. and I was always taught to keep quick sorting until you have made all the numbers pivots, but again I hope I wont get an examiner so pedantic to make me drop marks if I over pivot.
Thing is in Jan 10 Q5 output value is only 1 answer mark, there are other 4 method and answer marks for individual rows..

And the confusing thing in mark scheme is that for the first 4 box it is in one row, after that each box is in a single row..
13. (Original post by thephysicsguy)
Thing is in Jan 10 Q5 output value is only 1 answer mark, there are other 4 method and answer marks for individual rows..

And the confusing thing in mark scheme is that for the first 4 box it is in one row, after that each box is in a single row..
yeah theres no explanation in the edexcel textbook and online video guides give very different tutorials so all id say is get the right output
14. In a linear programming question it says determine the optimal value without saying maximum or minimum. I checked the answer and they find the maximum how come?
15. The answer is in the question. What is the objective of the linear problem? does it say that they are trying to maximise profit etc? If so optimal value will be maximum.
Post question and we can help further
16. In the 2nd part of route inspection questions where it says the postman can now start wherever he wants but must transverse every arc and wants to minimise his route how would you answer that, logic dictates that he would start and finish at either end of the shortest arc but that is always the wrong answer.
17. Say weight of network is 100
And these are the points you have to repeat
AC + BD = 10 + 20 = 30
AB + BC = 5 + 15 = 20
AD + CD = 25 + 30 = 55
The shortest edge is AB. So if you repeat AB then total is 100+5 = 105
But if you start at A and end at B then you have to repeat CD which is 30, which means total is now 100+30=130
You wanna repeat shortest edge as that will be added to total weight and mean you get least weight. Make sense?
18. you double up the arc of least weight leaving two nodes odd, these are the one's where you start/finish
19. (Original post by I witness I)
In the 2nd part of route inspection questions where it says the postman can now start wherever he wants but must transverse every arc and wants to minimise his route how would you answer that, logic dictates that he would start and finish at either end of the shortest arc but that is always the wrong answer.
If the postman can start and finish anywhere he wants, choose the lowest total weighed path of 2 odd vertices. The arcs in this path will be traversed twice. And the remaining 2 would be your starting and finishing points.
20. (Original post by WavingFLag)
Say weight of network is 100
And these are the points you have to repeat
AC + BD = 10 + 20 = 30
AB + BC = 5 + 15 = 20
AD + CD = 25 + 30 = 55
The shortest edge is AB. So if you repeat AB then total is 100+5 = 105
But if you start at A and end at B then you have to repeat CD which is 30, which means total is now 100+30=130
You wanna repeat shortest edge as that will be added to total weight and mean you get least weight. Make sense?
so to answer your question you would start and finish at b/c? sometimes they include questions where you add in a new road and I get that , the only thing im possibly worried about tomorrow is if a flowchart question comes up as im still not 100% sure how to fill it in, although getting the output is easy enough. Ive got an m1 resit straight after aswell so a big day tomorrow.

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