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# ocr mei d1 - how did everyone find it? watch

1. (Original post by Aired)
I see what you mean, but the question asked you to solve the problem graphically. You should have drawn in the contraints, shaded out the inappropriate regions, and then drew in the profit line. You then slide the profit line until it reaches the very last point inside the feasible region, which is the optimum point (and therefore your solution).

If you solved it using simultaneous equations, you would have ended up wit the answer giving the largest amount of product (I think), rather than the proportion of f:g produced that gives the highest profit.
I did draw it, but without the profit line, and I didn't draw it to scale, I just wanted to see where each constraints cross the axis, so then comparing the gradients of the constraints found x and y by simultneous equations.

I still don't agree: the question wouldn't ask for number of f and g to be produced if one of them is not to be produced in the first place.
Realistically speaking, have you ever come across a LP question where in the end one of the variable equals 0 in order to get max profit?
2. (Original post by Vijay1)
I did draw it, but without the profit line, and I didn't draw it to scale, I just wanted to see where each constraints cross the axis, so then comparing the gradients of the constraints found x and y by simultneous equations.

I still don't agree: the question wouldn't ask for number of f and g to be produced if one of them is not to be produced in the first place.
Realistically speaking, have you ever come across a LP question where in the end one of the variable equals 0 in order to get max profit?
Think about it this way...

f + 2g (less than or equal to) 25000.

Why would you use some of the 25,000 to produce 'f', which only has a profit of 9p when you could use it to produce more 'g' with a profit of 20?

The optimum point is always a corner of the feasible region, a corner against an axis is a corner all the same...
3. (Original post by Aired)
Think about it this way...

f + 2g (less than or equal to) 25000.

Why would you use some of the 25,000 to produce 'f', which only has a profit of 9p when you could use it to produce more 'g' with a profit of 20?
because it said the company manufactures the two (f and g), the company STRICTLY manufactures the two, the company doesn't want an optimal solution to go on and say STOP producing that. And I wouldn't think the company would stop producing it just for the sake of profit. A variable f or g wouldn't be discarded for the sake of profit.

That wouldn't be LP anymore, that would just be looking for the greatest coeffecient in front of the variables and setting the corresponding variable to 0, to get max profit:

(E.g maximise 4x + 20y, with your argument you would say, produce no x and produce all y, the amount of y - determined by the constraints)
Surely this would also give a max profit and may satisfy the constraints but is this really LP?
4. Well you had to give the amounts of g and f which satisfy the contraints, and give the maximum profit. To give the maximum profit, 'f' has to be 0...

If you're saying that the company HAS to manufacture both, the answer would just be '1 litre of f, 12499 litres of g' or something similar.
5. (Original post by Aired)
Well you had to give the amounts of g and f which satisfy the contraints, and give the maximum profit. To give the maximum profit, 'f' has to be 0...

If you're saying that the company HAS to manufacture both, the answer would just be '1 litre of f, 12499 litres of g' or something similar.
Fair enough, I don't see point in discussing this further without the accurate information of the constraints and profit equation.
Well, if I did question 6, wrong then I must have failed
6. (Original post by Vijay1)
Fair enough, I don't see point in discussing this further without the accurate information of the constraints and profit equation.
Well, if I did question 6, wrong then I must have failed

I really wouldn't worry about it, you could be correct and I could be wrong. Even if you have got the wrong optimal solution, you'll still get the carry though marks, marks for producing the contraints, and drawing the graph.
7. (Original post by Aired)
I really wouldn't worry about it, you could be correct and I could be wrong. Even if you have got the wrong optimal solution, you'll still get the carry though marks, marks for producing the contraints, and drawing the graph.
In the end, I hope we've both done well regardless of question 6
8. Just to clear things up... my question 6:

maximise p = 9f + 20g
subject to
½f + 3/4g « 12000 Nutrients mix
f + 2g « 25000 litres of each

drawing this graphically, I observe the intersection of the two constraints at a point:

By simultaneous equations:

f = -2g + 25000
sub f into second equation:

½(-2g + 25000) + 3/4g « 12000
expanding
-¼g + 12500 = 12000
g = 2000
sub g back into the constraint to get f = 21000

sub g and f in p to get profit
9(21000) + 20(2000) = 229000p = £2290

To do a final check with f and g suitable for constraints:

sub f and g into ½f + 3/4g to get value less then 12000

½(21000) + 3/4(2000) = 12000 hence satisfies constraint

sub f and g into f + 2g to get value less then 25000

21000 + 2(2000) = 25000

The max profit as above and all the constraints are satisfied to the max by
f = 21000 and g = 2000

I I was checking one of the minor vertices in the feasible region, so the highest profit would be £2500 by f = 0 and g = 12500

Oh well
9. Just to add my view...
For the LP question I got it lying on the axis, with no F produced. And I got 12 and 14 for the first question too.
10. (Original post by Vijay1)
Just to clear things up... my question 6:

maximise p = 9f + 20g
subject to
½f + 3/4g « 12000 Nutrients mix
f + 2g « 25000 litres of each

drawing this graphically, I observe the intersection of the two constraints at a point:

By simultaneous equations:

f = -2g + 25000
sub f into second equation:

½(-2g + 25000) + 3/4g « 12000
expanding
-¼g + 12500 = 12000
g = 2000
sub g back into the constraint to get f = 21000

sub g and f in p to get profit
9(21000) + 20(2000) = 229000p = £2290

To do a final check with f and g suitable for constraints:

sub f and g into ½f + 3/4g to get value less then 12000

½(21000) + 3/4(2000) = 12000 hence satisfies constraint

sub f and g into f + 2g to get value less then 25000

21000 + 2(2000) = 25000

The max profit as above and all the constraints are satisfied to the max by
f = 21000 and g = 2000
I could be wrong here, because I don't really remember the question very well, but wasn't it 0.75f + 0.5g for the nutrient mix?
11. (Original post by sonja)
I could be wrong here, because I don't really remember the question very well, but wasn't it 0.75f + 0.5g for the nutrient mix?
No.
12. i cant help but notice that no one has mentioned how crap question one was
dat was such a dumb question- wot da hell were u supposed 2 do????
i think i messed by LP up aswell.

one thing dat i didnt like was da fact that the questions kept on asking you to justify your answer???? they were worth 2 marks and i had no clue on wot 2 write?
dis paper was crapper than all the practise ones id done.
13. (Original post by darth_vader05)
i cant help but notice that no one has mentioned how crap question one was
dat was such a dumb question- wot da hell were u supposed 2 do????
i think i messed by LP up aswell.

one thing dat i didnt like was da fact that the questions kept on asking you to justify your answer???? they were worth 2 marks and i had no clue on wot 2 write?
dis paper was crapper than all the practise ones id done.
Thats not true, this paper was nice and if more time easy. I didn't do the practise papers, there always different to the real exam!
But the maze question got me thinking, I mean who could have thought of getting to the other end by following the side walls?

Btw, to justify the maze questions you would say that the maze can be represented by a graph with the edges being the walls and the nodes being the dead ends, so the maze is a uncomplete graph hence following the walls/ edges will always lead to the exit.
LP question, I thought I got right, but after all I must have got it wrong, but I'll get about 4-5 marks in that atleast.

I missed the very last part of the simulation question, otherwise it was fine.
14. (Original post by Vijay1)
Thats not true, this paper was nice and if more time easy. I didn't do the practise papers, there always different to the real exam!
But the maze question got me thinking, I mean who could have thought of getting to the other end by following the side walls?

Btw, to justify the maze questions you would say that the maze can be represented by a graph with the edges being the walls and the nodes being the dead ends, so the maze is a uncomplete graph hence following the walls/ edges will always lead to the exit.
LP question, I thought I got right, but after all I must have got it wrong, but I'll get about 4-5 marks in that atleast.

I missed the very last part of the simulation question, otherwise it was fine.
wot about question 1???
it said sommer about a junction box and i rote some mumbo jumbo about electrictiy!
well one things for sure, i didnt get no justify questions right
15. (Original post by darth_vader05)
wot about question 1???
it said sommer about a junction box and i rote some mumbo jumbo about electrictiy!
well one things for sure, i didnt get no justify questions right
Don't be negative 'Its gona be fine'

because normally the grade boundaries are set very low for D1.
That question 1, I wrote that a junction box allows all the nodes to be connected to only one node (and maybe distance of edges are reduced)
16. (Original post by Vijay1)
Don't be negative 'Its gona be fine'

because normally the grade boundaries are set very low for D1.
That question 1, I wrote that a junction box allows all the nodes to be connected to only one node (and maybe distance of edges are reduced)
i missed part (i) out cos i didnt know how to draw it. its a bit hard not to be negative when u know uve messed up and when u know uve not got an A

2day we started M2 and dats a load of bull aswell. we were doing sommer about friction!!! theyve already started next yrs work
17. I found it overall quite easy, but I didn't realise you should have turned right around at dead ends in the maze question, so I've lost about 6 marks from that question.
18. (Original post by darth_vader05)
i missed part (i) out cos i didnt know how to draw it. its a bit hard not to be negative when u know uve messed up and when u know uve not got an A

2day we started M2 and dats a load of bull aswell. we were doing sommer about friction!!! theyve already started next yrs work
Well most schools are meant after the AS exams, starting the A2 right away, because A2 modules contain more work and need more time.

Your lucky to do M2, We should have started M1 last week but the new syllabus books haven't arrived, so we have to work through a Higher GCSE text book boring, totally time-wasting
19. (Original post by Vijay1)
Well most schools are meant after the AS exams, starting the A2 right away, because A2 modules contain more work and need more time.

Your lucky to do M2, We should have started M1 last week but the new syllabus books haven't arrived, so we have to work through a Higher GCSE text book boring, totally time-wasting
lucky
id prefer 2 do differential equations first.
we're probs gonna start FP2 aswell.
mechancis has sooooooo much physics involved and i hate physics!

are you in AS?? cos u said dat ur doin D1 retake and ur doinn C1 etc
20. (Original post by darth_vader05)
lucky
id prefer 2 do differential equations first.
we're probs gonna start FP2 aswell.
mechancis has sooooooo much physics involved and i hate physics!

are you in AS?? cos u said dat ur doin D1 retake and ur doinn C1 etc
Well I did AS Math and further math: In math I've done C1, C2, S1 and in further math D1, S2, FP1 and D1 didn't go well in january so I resat.

For A2, we'll do C3, C4, M1 and in further math FP2, NM, FP3 or S3

I love physics, all though I don't do it, I enjoyed it at GCSE. I would say if you enjoy math then surely you'll enjoy Physics hence Mechanics

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