Urgent D1 help

I hate D1.

http://www.ocr.org.uk/download/pp_07_jun/ocr_18161_pp_07_jun_l_gce.pdf

Question 2. Where does the constraint f>/= 20 come from? I get the d constraint and the g etc.

I hate linear programming. :frown:

Reply 1

Ste2210

where is this constraint mentioned in the question?

Reply 2

tommy1311

http://www.ocr.org.uk/download/ms_07/ocr_16329_ms_07_l_gce_jun.pdf

It's in the mark scheme as the answer. It asks for a feasible value, but that means a minimum feasible value for the area of flowers, which is f. The only link I can work out is that it COSTS £20 for a square metre of flowers, but that isn't the same.

Reply 3

Ste2210

ah i see, ok so the toal area is 120, we know that at least 40 is grass, the grass cannot exceed 4 times the amount of decking, and also that there cannot be more decking than flowers, so, as its simplest ratio of grass:decking:flowers we get 4:1:1
4+1+1=6
120/6=20
grass=4*20=80
decking=1*20=20
flowers=1*20=20

Reply 4

tommy1311

Yeah I get that now. Seems a bit twisty for a small-mark question (which seems to be all the rage in D1). Thanks!

Reply 5

Ste2210

haha no probs, and yeah they do love their 2 mark/3 marl questions don't they! how are u feeling bout the exam tommorow? need any more help just ask

Reply 6

tommy1311

I've got:

Minimum Connectors
Travelling Salesperson
Route inspection
Simplex
Sorting
First fit/decreasing
Djikstra's

Down to a T. I struggle with elements of

Graph Theory
Liner Programming

The small-mark questions on order of nodes etc. get me everytime. :frown:

So it's not looking THAT great, but I'm confident I can really nail the other parts.

Reply 7

Ste2210

ok with L.P the only things you can really do to help your self is knowing how to use y=mx+c and to then change to an inequality, then to also b able to put values in to the objective function to find a MAX or MIN, as for graph theory, it changes with every exam and it depends entirely on the question as to whether i even try and answer it or not haha, i did a horrible practice one today but then sometimes theyre simples!

Reply 8

Ste2210

i would suggest that on a question such as "explain why this graph cannot be achieved" you should attempt drawing the graph in order to visualise why it cannot be achieved

Reply 9

tommy1311

I understand using the vertices and picking out the largest/smallest integer/non-integer answer etc. It's more being asked to pick out the constraints and stuff which irritates me. Hopefully the big questions will be on Djikstra's or Simplex. Thanks for the help! Are you sitting the exam tomorrow?

Reply 10

Ste2210

OMG! please tell me u found the exam as impossible as i did! lmao, the last 3 questions were horrible!!

Reply 11

tommy1311

It was absolutely disgusting. Spent too much time on the algorithm question, mixed my simplex up and was going to come back to it, but ran out of time before I had a chance to even finish the last question! Didn't get a lot of it right either. Very surprised if I have Anything over a C for that. In fact, I'd put my house on it.

Reply 12

Ste2210

yeah i didnt realise you only had to record R and S in the algorythm thing so i wrote the whole thing out lol, and as for the simplex thing, i think i got it right, it was just too long! 2 iterations and 4 variables!!! the last question was ridiculous, why did they have to stick that stupid x in place of a number!!