Edexcel D1 question help, please!

Can someone please help me on question 7, thanks, I worked out the intersection of 3x=2y and 5x + 4y = 80, I got what the mark scheme has but their x is my y and my x is their y so I don't know what I'm doing wrong?, I figured that if you workout the intersection of y > 6 and 5x + 4y = 80 then you get the mark schemes answer but,isn't the y> 6 a inequality and not a line? therefore it doesn't make sense to find an intersection. PLEASE HELP, I'M WORRIED ABOUT THE EXAM, thanks!! =D
http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/june2010-ms/6689_01_msc_20100618.pdf

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/june2010-qp/6689_01_que_20100527.pdf

Reply 1

Fortitude

Original post by Skilled

Hi, y>6 is already on the graph & shaded in & the optimal point is the intersection point of 3x=2y & 5x+4y=80. :smile:

Reply 2

Dilzo999

y isn't included so you have to use integer testing to find the correct point which works.

Reply 3

Skilled

Original post by Fortitude

Hi, y>6 is already on the graph & shaded in & the optimal point is the intersection point of 3x=2y & 5x+4y=80. :smile:

I worked out the intersection of 3x=2y and 5x + 4y=80 but I got (7,11) but the mark scheme says (11,7)

Reply 4

Skilled

Original post by Dilzo999

y isn't included so you have to use integer testing to find the correct point which works.

sorry but i dont understand what you mean

Reply 5

Fortitude

Original post by Skilled

I worked out the intersection of 3x=2y and 5x + 4y=80 but I got (7,11) but the mark scheme says (11,7)

Hi, You were right, I just realised that there's a vertex at y=6 so that would be the optimal point hence it'd be the intersection of y=6 & 5x+4y=80, sorry for mistake :colondollar:

which gives you (11.2, 6) (I used simultaneous equations to calculate this or you could read from the graph but mine's not that clear) Now as you said, you can't include y=6 so the next integer would be 7 hence then answer (11,7) & you could also test out other integers which are close to it as well to find the optimal solution but be careful to see if they're feasible or not. :biggrin:

Reply 6

Skilled

Original post by Fortitude

Hi, You were right, I just realised that there's a vertex at y=6 so that would be the optimal point hence it'd be the intersection of y=6 & 5x+4y=80, sorry for mistake :colondollar:

Thanks, I get it now! =D , I have not seen a tricky question like this before

Reply 7

Fortitude

Original post by Skilled

Thanks, I get it now! =D , I have not seen a tricky question like this before

You're welcome :biggrin:

Reply 8

Skilled

Original post by Fortitude

You're welcome :biggrin:

Please help

When it says I can start and end at any point in a Chinese postman question, how do you workout those points? and if it gives you a start and tells you to end at any point then what do you do? what if it gives you an end and tell you to choose a start?

Thanks in advance

Reply 9

Fortitude

Original post by Skilled

I'll try my best to explain but if you have a specific Q please post it as it'd probably make more sense. Anyway for eg you've found that you need to repeat the arcs A,C,D,G:

AC + DG = 45 + 20 =65
AD + CG = 22 + 46 = 68
AG + CD = 35 + 29 = 64

If you're told to start at G & you need to find where to finish & which arcs to repeat pick the arcs which give you the shortest path, here it will be AD (don't include DG becuase G is your starting vertex so no need to repeat) & therefore you'll finish at C. :smile:

Reply 10

Skilled

Original post by Fortitude

yup, i understand, one last doubt, what if i had to choose a start and end point for this example

Reply 11

Fortitude

Original post by Skilled

yup, i understand, one last doubt, what if i had to choose a start and end point for this example

Then you just look at which path is the shortest, here it's DG (20) therefore you'd repeat DG & start & finish at A & C

Reply 12

Skilled

Original post by Fortitude

Then you just look at which path is the shortest, here it's DG (20) therefore you'd repeat DG & start & finish at A & C

thanks!, I can't give you rep because it doesn't let me =(

Reply 13

Fortitude

Original post by Skilled

thanks!, I can't give you rep because it doesn't let me =(

You're welcome :biggrin:

Reply 14

Zeionic

Here are some notes I created! Feel free to download them :smile:

D1.pptx

Reply 15

Skilled

Original post by Fortitude

You're welcome :biggrin:

When it gives you an equation eg. 6x + 9y = P max, then does the graph cross at (0,6) and (9,0) ? is it always the coordinates of each other?

Reply 16

Fortitude

Original post by Skilled

When it gives you an equation eg. 6x + 9y = P max, then does the graph cross at (0,6) and (9,0) ? is it always the coordinates of each other?

Is this an objective line?

Reply 17

Skilled

Original post by Fortitude

Is this an objective line?

yup

Reply 18

Fortitude

Original post by Skilled

When it gives you an equation eg. 6x + 9y = P max, then does the graph cross at (0,6) and (9,0) ? is it always the coordinates of each other?

What I've been taught is to choose a no that is a multiple of 6 & 9 for eg 360 & put in into the equation so 6x + 9y = 360 & use this to work out coordinates so here it could be (0, 40) & (60, 0). It doesn't matter which no you use as long as it's a multiple & it obvs depends on scale of the axis because it'd be no use using 360 if the scale on the axis was from 2550 to 8000 :tongue: