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Arsey's D2 S14 Model Answers (R) added

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Original post by Arsey
solving transportation problems using simplex tableau is not in the D2 specification


What is this supposed to mean? Either the LP problem gives the correct answer or not. It doesn't if you use all <= constraints. If you were to try and actually solve a transportation problem using LP, using your method, you would get C=0; which is wrong.
Reply 81
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Original post by metaltron
I have explained this all before though. I showed you the examples using => constraints, and they all resulted in the correct solution to the transportation problem. I explained how using => is the same as loosening the = constraints that you say are acceptable.

What isn't acceptable is using all <= constraints, because you get the wrong answer... C = 0.

Also, I must add I have used some <= inequalities, to ensure that we do not transport more than is in stock; so this is not a problem at all and I don't know why you keep referring to it.

As for demand, the demand must be met (so use = or =>) but you cannot allow us to not meet the demand within the constraints (<=) because this leads to C=0.


Well we will agree to disagree, because you are wrong.

When the MS is released you can write to Edexcel to complain to see if you get any joy from them, when you don't I suggest you start an online petition, they seem popular.
Original post by Arsey
Well we will agree to disagree, because you are wrong.

When the MS is released you can write to Edexcel to complain to see if you get any joy from them, when you don't I suggest you start an online petition, they seem popular.


I'm not happy to agree to disagree, since that is cowardly. I have given you a maths argument which you will not respond to because it is not in the D2 spec which I find a sickening excuse, because it is so typical of the A-level system.
Original post by Arsey
Well we will agree to disagree, because you are wrong.

When the MS is released you can write to Edexcel to complain to see if you get any joy from them, when you don't I suggest you start an online petition, they seem popular.


I would complain to Edexcel but without the support of a teacher, such as yourself, it would most likely be fruitless; I know that OCR refuse to discuss mark schemes outright, I'm not sure whether that is true for Edexcel or not.
Reply 84
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Original post by metaltron
I'm not happy to agree to disagree, since that is cowardly. I have given you a maths argument which you will not respond to because it is not in the D2 spec which I find a sickening excuse, because it is so typical of the A-level system.
:smile::rolleyes::moo:


https://www.facebook.com/EdexcelStudents

https://twitter.com/EdexcelStudents

[email protected]

http://www.edexcel.com/iwantto/Pages/form-complaint.aspx



give it a shot, you never know.... well I do but.... :banana:
(edited 9 years ago)
Reply 85
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Original post by metaltron


As for demand, the demand must be met (so use = or =>) but you cannot allow us to not meet the demand within the constraints (<=) because this leads to C=0.


what if it is unand demand exceeds stock :angry::angry::angry::angry: nooooooo
(edited 9 years ago)
Original post by Arsey
what if it is balanced and demand exceeds stock :angry::angry::angry::angry: nooooooo


Yeah as I said a few posts back, then my LP problem would not have a solution, since the stock inequalities and the demand inequalities come to hate each other :tongue:

This is to be expected, since when there is more demand than stock, the transportation problem has no solution; unless you are saying it does.

I'll give you the benefit of the doubt with your 'balanced AND demand exceeds stock' comment :wink:
Original post by Arsey
what if it is unand demand exceeds stock :angry::angry::angry::angry: nooooooo


It goes without saying that your method would quickly yield the C=0 'solution'... :rolleyes:
Original post by Arsey


Well I've emailed them about it, but I am 99% sure I will be told I am not allowed to make 'subject-specific enquiries' :frown:

Have you got any suggestions on how I might be able to speak directly with the Maths department?
(edited 9 years ago)
Reply 89
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Original post by metaltron
Well I've emailed them about it, but I am 99% sure I will be told I am not allowed to make 'subject-specific enquiries' :frown:

Have you got any suggestions on how I might be able to speak directly with the Maths department?


I hate to say I told you so....



������


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(edited 9 years ago)
ImageUploadedByStudent Room1404658345.470809.jpg93.4KB
Original post by Arsey
I hate to say I told you so....

ImageUploadedByStudent Room1404658345.470809.jpg

😢


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Arsey how did you find this??? As that's this years mark scheme is it not?
Original post by Arsey
I hate to say I told you so....

ImageUploadedByStudent Room1404658345.470809.jpg




Posted from TSR Mobile


Hmm it's a slight improvement on the old mark scheme with the = sign being preferred but its still shocking to see.

I have already explained why it is wrong to use all <= constraints; and I think you secretly can see where I am coming from (C=0 shouldn't be the solution).

I can't see any justification for their rejection of the => constraints, which would be the correct loosening of the equals constraints (for demand).

I hope that my e-mail will reach them but if not I'm not sure how else I can get in touch; any suggestions? Otherwise I can't really do much.
Original post by metaltron
Hmm it's a slight improvement on the old mark scheme with the = sign being preferred but its still shocking to see.

I have already explained why it is wrong to use all <= constraints; and I think you secretly can see where I am coming from (C=0 shouldn't be the solution).

I can't see any justification for their rejection of the => constraints, which would be the correct loosening of the equals constraints (for demand).

I hope that my e-mail will reach them but if not I'm not sure how else I can get in touch; any suggestions? Otherwise I can't really do much.


I don't suppose you know how arsey has access to this years mark scheme already?
Original post by direland3
I don't suppose you know how arsey has access to this years mark scheme already?


I guess he knows somebody who marks D2, or perhaps the mark schemes are now out for teachers.
Original post by metaltron
I guess he knows somebody who marks D2, or perhaps the mark schemes are now out for teachers.


I hope he uploads the whole thing and from others too. There's some stuff I need clearing up on C4 and FP2
Original post by direland3
I hope he uploads the whole thing and from others too. There's some stuff I need clearing up on C4 and FP2


I hope the mark schemes work out for you then! They were both quite hard from memory, so I think the mark schemes will be in high demand.

I'm hesitant as to whether to post this, but I've always wanted to try making one of these! :tongue:

http://www.youtube.com/watch?v=xvKYddiisGk
Original post by metaltron
I hope the mark schemes work out for you then! They were both quite hard from memory, so I think the mark schemes will be in high demand.

I'm hesitant as to whether to post this, but I've always wanted to try making one of these! :tongue:

http://www.youtube.com/watch?v=xvKYddiisGk


Thank you. All I need to check on the FP2 was the complex no. question as I managed to show that for part a but I was doing it in a rush and I want to see if I got all the correct points down that would get me marks, so fingers crossed.
Original post by direland3
Thank you. All I need to check on the FP2 was the complex no. question as I managed to show that for part a but I was doing it in a rush and I want to see if I got all the correct points down that would get me marks, so fingers crossed.


Hopefully I'm thinking of the same question:

If you got the correct coefficients (a, b and c), you will surely get all 6 marks. The answer wasn't fully printed.
Original post by alexmufc1995
Hopefully I'm thinking of the same question:

If you got the correct coefficients (a, b and c), you will surely get all 6 marks. The answer wasn't fully printed.


I got the same answer as Arsey, but as it's a show that I want to make sure I dd enough steps to "show that" if I make sense
Reply 99
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Original post by metaltron
Hmm it's a slight improvement on the old mark scheme with the = sign being preferred but its still shocking to see.

I have already explained why it is wrong to use all <= constraints; and I think you secretly can see where I am coming from (C=0 shouldn't be the solution).

I can't see any justification for their rejection of the => constraints, which would be the correct loosening of the equals constraints (for demand).

I hope that my e-mail will reach them but if not I'm not sure how else I can get in touch; any suggestions? Otherwise I can't really do much.


hardly shocking, I told you this is exactly what it would say = (because it is balanced) but it would accept <=

You have left it too late, you should have paid more attention to the text book.

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