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Edexcel D1 - 17th June, 2016 [Exam discussion]

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Original post by target21859
Here's the mark scheme


June 2014, final question? What a nightmare :s-smilie:
Original post by SeanFM
June 2014, final question? What a nightmare :s-smilie:


Yeah I thought I understood but I just realised I actually don't. If you know how to do it could you explain it to me please? There's different methods such as point testing and the gradient of the line but I don't understand either of them.
Original post by target21859
Yeah I thought I understood but I just realised I actually don't. If you know how to do it could you explain it to me please? There's different methods such as point testing and the gradient of the line but I don't understand either of them.


I sat the exam and left this question blank :lol: I'll have a look again, I thought someone explained it above.
Original post by SeanFM
I sat the exam and left this question blank :lol: I'll have a look again, I thought someone explained it above.


Yeah partially. He gave me a hint as to how to go about it and I thought that I solved it but I just realised that I didn't. I think the grade boundaries were quite low that year. It was like 71 for full ums.
Original post by target21859
Yeah partially. He gave me a hint as to how to go about it and I thought that I solved it but I just realised that I didn't. I think the grade boundaries were quite low that year. It was like 71 for full ums.


Well you know that the function at A is less than D so that's your first inequality.. you somehow have to deduce that C is less than B, but not sure how :tongue: seems countet intuitive if you look at the graph.
Original post by target21859
Yeah partially. He gave me a hint as to how to go about it and I thought that I solved it but I just realised that I didn't. I think the grade boundaries were quite low that year. It was like 71 for full ums.


The profit line can be between the gradient BA and CD, if it were any steeper, then it would cross B first, if it were any shallower, it would C last. The gradient of BA is -4 and the gradient of CD is -2.

Now,the profit line can be written as, y=−1kx+α y= -\frac{1}{k}x+ \alpha where α\alpha is some constant, so the gradient of the profit line is −1k-\frac{1}{k}


This can be between the gradient of BA and CD, it can't equal these gradients however, as the profit line would cross all points on the line, meaning all points on the line would be the minimum/maximum.

So,−4<−1k-4<-\frac{1}{k} and −1k<−2-\frac{1}{k}<-2. Rearrange the inequalities , remembering to reverse the inequality sign when multiplying or dividing by a negative number.
Original post by NotNotBatman
The profit line can be between the gradient BA and CD, if it were any steeper, then it would cross B first, if it were any shallower, it would C last. The gradient of BA is -4 and the gradient of CD is -2.

Now,the profit line can be written as, y=−1kx+α y= -\frac{1}{k}x+ \alpha where α\alpha is some constant, so the gradient of the profit line is −1k-\frac{1}{k}


This can be between the gradient of BA and CD, it can't equal these gradients however, as the profit line would cross all points on the line, meaning all points on the line would be the minimum/maximum.

So,−4<−1k-4<-\frac{1}{k} and −1k<−2-\frac{1}{k}<-2. Rearrange the inequalities , remembering to reverse the inequality sign when multiplying or dividing by a negative number.


Thank you that explained it really well. It was really appreciated.
What definitions do we need to know?
For activity networks, does the number ordering for the nodes matter?
Original post by Nikhilm
For activity networks, does the number ordering for the nodes matter?


For constructing them no, the dependencies have to be correct. For Critical Path Analysis, the order of labelling matters.
(edited 7 years ago)
Original post by Jules12345
What definitions do we need to know?


https://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Specification%20and%20sample%20assessments/UA035243_GCE_Lin_Maths_Issue_3.pdf

Page 100
Original post by NotNotBatman
For constructing them no, the dependencies have to be correct. For Critical Path Analysis, the order of labelling matters.


Thanks! Would you get marks deducted for curvy lines when constructing?
Original post by Nikhilm
Thanks! Would you get marks deducted for curvy lines when constructing?


No, that would be fine.
Original post by NotNotBatman
No, that would be fine.


How sure are you about that? Cos a couple of mark schemes have drawn curvy lines, but the book says the convention is straight lines and I remember seeing an examiners report discouraging curvy lines, I'll try and find a link to it
Original post by Nikhilm
How sure are you about that? Cos a couple of mark schemes have drawn curvy lines, but the book says the convention is straight lines and I remember seeing an examiners report discouraging curvy lines, I'll try and find a link to it


I've seen about 4 questions asking for the construction of an activity network, in the marking scheme it never says anything about curvy lines, whats marked are the dependencies and dummies. My teacher has also told me that it doesn't matter.
can someone link me the 2015 d1 paper with the answer booklet and mark scheme please?
Original post by HarveySpecter97
can someone link me the 2015 d1 paper with the answer booklet and mark scheme please?


http://qualifications.pearson.com/content/dam/pdf/A-Level/Mathematics/2013/Exam-materials/6689_01_que_20150609.pdf
when formulating a linear programming problem, are you supposed to put the whole summary like when it says: minimise/maximise "objective function"
subject to: "constraints"

even if you've wrote it out before hand? idk if people know what i mean, like in edexcel textbooks for example page 118 from example 3, they've basically wrote the decision variables, objective function and constraints and then summarised it in the subject to stuff. :smile:
Original post by NotNotBatman
I've seen about 4 questions asking for the construction of an activity network, in the marking scheme it never says anything about curvy lines, whats marked are the dependencies and dummies. My teacher has also told me that it doesn't matter.

How about lines that cross over each other?
Hey guys how do I schedule a project without a gantt chart beforehand? An example is this question part D!
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