D1 (Decision 1) 17 May 2013 Official Thread

Scroll to see replies

Yes you can do the paper in pencil but to be safe I'd do any written answers in pen, and diagrams in pencil

ignore the invigilators, pencil is fine. If the marker cannot read your work they have to mark the actual paper.

However, I would say your advice is dangerous because on the scan, only the pen might show up and the marker may not notice faint pencil lines.

if you are using a pencil use a good HB! :wink:

You could use one of those black pens that rub out, work of the devil but useful in D1.

Reply 681

Arsey

Original post by Flounder1

I really really don't want scheduling diagrams to come up but it looks likely :frown:

Posted from TSR Mobile

hardly likely it has only ever been on one of the current spec papers, before that it was on in about 2007?

My money is on a Gantt.

Scheduling is horrible to mark.... Gantt is much easier to mark...

Reply 682

posthumus

Guys silly question, but thought I'd better be safe than sorry....

When you do Dijkstra, the space underneath the 3 boxes is for like working out or keeping track or whatever :tongue:

...
Are those also marked ? Because I usually leave mine empty.

Thanks in advance :smile:

EDIT: Oh wait, looking back I think this may have already been answered :tongue:

I think I will leave them blank? Y/N :redface:

(edited 10 years ago)

Reply 683

ambbs

Original post by Arsey

Scheduling is horrible to do as well so I hope it doesn't come up!
Have you got any general tips for linear programming? I know you said to concentrate on it because it's one of the harder parts, so I've done loads of questions but I always make silly mistakes, especially when you get given something in context and have to turn it into an inequality...took me quite a while to figure out the Jan 13 one!

Posted from TSR Mobile

Reply 684

Arsey

Original post by Revengeissweet

Did pretty much all available- don't even ask.. we got one every week.
With the answer book and the questions its been a lot of paper..
marks vary from 67-71- gotta watch out on stupid mistakes though, like not answering parts of questions :rolleyes:

On one of the past D1 revision threads I uploaded all of the old spec D1 papers which I had adapted to the new spec.

http://www.thestudentroom.co.uk/showthread.php?t=1865487

I uploaded lots of stuff to this thread, check it out.

The more papers you do the better. I would also advise doing the exam style paper in the book and the review exercises.

There are even Solomon D1 papers for the truly dedicated.

Reply 685

Pebbles94

Original post by posthumus

Guys silly question, but thought I'd better be safe than sorry....

When you do Dijkstra, the space underneath the 3 boxes is for like working out or keeping track or whatever :tongue:

...
Are those also marked ? Because I usually leave mine empty.

Thanks in advance :smile:

EDIT: Oh wait, looking back I think this may have already been answered :tongue:

I think I will leave them blank? Y/N :redface:

"It is essential that the working values are listed in the correct order if the candidates are to gain full credit." From an examiners report, so yes you need working values :smile:

Reply 686

Arsey

Original post by ambbs

the best tip I can give you is not to get it right otherwise you will lose almost all the following marks.

Practise the questions that are just about forming the problem.

Reply 687

posthumus

Original post by Pebbles94

"It is essential that the working values are listed in the correct order if the candidates are to gain full credit." From an examiners report, so yes you need working values :smile:

Aaaahhhh damn it ! :frown:

But what do they mean by "correct order" :confused:

& Thanks for the response ! :smile:

Reply 688

Arsey

Original post by Pebbles94

"It is essential that the working values are listed in the correct order if the candidates are to gain full credit." From an examiners report, so yes you need working values :smile:

this is true; however, you only need to put down additional working values if they are smaller than what you already have.

Reply 689

Anythingoo1

Original post by Arsey

You could use one of those black pens that rub out, work of the devil but useful in D1.

Haha ok thanks dude, just went out and brought 5 HB pencils the other day aswell

Can you help me with something in D1? I don't understand how you're meant to draw the objective lines. am I right in understanding that the objective line doesn't have to fall in the feasible region? And how do you go about drawing it?

If you need a specific example I can link you a question in a past paper :smile:

Reply 690

otrivine

Original post by Arsey

But sir the solomon are hard and use knowledge of work we have not done

Reply 691

Arsey

Original post by Anythingoo1

I think the easiest way of doing it is as follows

say the objective is

P = 30x + 50y

simply swap the numbers so x = 50 and y = 30, mark these on the axes and join.

if 50 and 30 do not work very well on your graph, too big or too small, double them or halve them etc.

The objective line doesn't have to fall in the feasible region, normally it doesn't.

DON'T FORGET TO LABEL IT!

Reply 692

posthumus

Original post by Arsey

the best tip I can give you is not to get it right otherwise you will lose almost all the following marks.

Practise the questions that are just about forming the problem.

Hello Sir,

I also have a feeling that linear programming will be the most horrible question in this paper! Do you have any idea how hard a linear programming question can get though ?

I so far find the bit where they want integer values;
What do I do when I get my 2 non-integer co-ordinates x & y using the objective line? Do I do a table and test all possibilities (for lets say [11.7,3.2]) :

(12,3)
(11,3)
(12,4)
(11,4)

??? :smile:

I also believe that sometimes you may need to figure out yourself that your "objective value" (please correct me on my use of term :tongue:

) will be an integer ? :smile:

Thanks in advance !

Reply 693

Arsey

Original post by otrivine

But sir the solomon are hard and use knowledge of work we have not done

I agree with you to a certain extent. The Solomon ones are based on old spec, so I went through them and binned all flows and simplex and currect spec questions that were just stupidly hard.

Most of the Solomon questions are fine and help prepare you for the awkward Edexcel questions.

Reply 694

Better

Original post by Arsey

Things just got serious. Arsey is here. :eek4:

Arsey is there a faster way to do Linear Programming Vertex Testing. I just did January 2013 and I finished on time but the Vertex Testing took me a very long time.

Any help would be appreciated.

Reply 695

lijojohn08

Heyyy pleasee help me guys, quick questions:
1) if an inequality is strict and you draw it on the graph... when you find the intersection to get the coordinates would be be IN the feasible region or not? if not how would you find the optimal solution if you have a strict inequality (Sorry that might be a bit confusing :colondollar:

)

2) When you follow a flow chart... when you you start a new line on a trace table? are there marks for getting the correct lines?

Reply 696

Arsey

Original post by posthumus

I also believe that sometimes you may need to figure out yourself that your "objective value" (please correct me on my use of term :tongue:

) will be an integer ? :smile:

Thanks in advance !

If the objective point is a decimal and you require an integer solution (they don't always make it clear you need an integer solution by the way), then it is most likely you will be able to simply mark on the integer solutions inside the feasible region close to the objective point. Then use the ruler method again.

However, make sure you state the decimal solution even if it is obvious it isn't valid.

You have never needed to use the method you wrote about and I would agree that would be about as hard as it gets. What you need to do is test those points against the constraints which intersect to give you the decimal objective point.

say for example one constraint was x > 3y

in your example the 3rd and 4th coordinates do not satisfy this constraint so would not be in the feasible region. 99% of the time 3 fail one or both constraints leaving you with the correct answer.

The biggest mistakes made on LP questions are not forming the constraints correctly and drawing the objective line incorrectly (so obj = 30x + 20y, muppets will join 30 on the x-axis to 20 on the y-axis).

Reply 697

Anythingoo1

Original post by Arsey

Ok thanks alot! Also just to be sure, say the objective line was P = 5x + 7y, and your graph went up in all the way to 60 on both axes, would it be ok to double it (x = 14, y = 10) ?

Reply 698

Vaner

Original post by Arsey

Do you suggest doing solomon now? Also just to clarify, I can do diagrams in pen or pencil?

Thank you!

Reply 699

Arsey

Original post by lijojohn08

)

2) When you follow a flow chart... when you you start a new line on a trace table? are there marks for getting the correct lines?

technically no, but on one of the past papers they accepted solutions on the dotted line in the answers.

2. flows is unlikely to be on as the sorting algorithms have to be on but it doesn't matter.