D1 (Decision 1) 17 May 2013 Official Thread

I did May 2009 paper and just wanted to ask a question..for question 3, Bipartitate graph..the c part..starting from E, does it have to go all the way to 6 like they did in the mark scheme or can I do

E-5=r-4 then cs

then from h-1=s-3=c-6
then you get the same answer...?

http://www.mathsgeeks.co.uk/pdf/C2Ed...elJune09MS.pdf

you mean the solomon, the questions the way they are structured is quite different in our text book questions and edexcel papers/

Yh, but you know that question we had in January... the first question was horrible, do you think that flow stuff could come up again ??

Would have helped if the link works

I think your going wrong because your looking at figure 2 & not at what you got in part a)

Just realised. Thanks

Of course, they are!

I'm worried about making a mistake in the exam, because I know that would be deadly in decision since the following questions always stem from the first (e.g inspection, CPA, Dijkstra's). Especially because I was making silly mistakes in the mechanics exam, but fortunately, I had enough time to check, idenify and correct them.

I'm stuck on part e) Why wouldn't reducing activity "I" not make it profitable??

Thanks in advance


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can you explain to me part d) ?

For each day day the project is delayed you get £50,000 fine

now activity F is delayed by 3 days... since its critical, the whole project is delayed by 3 days

therefore fine = 3 x 50,000 = £150,000

If you reduce N by 1 day, since it's critical you'll save 1 day on whole project, so overall it will only be 2 days delayed... so your fine would be 2 x 50,000 = £100,000

saving you £50,000

however to reduce activity N by 1 day it costs £90,000

therefore your savings are outweighed, and you make a net loss of 90,000 - 50,000 = £40,000

So your £40,000 better off if you just delay the project by 3 days

when you are doing doing a binary search for names, it is important to write out the full names of the people involved? for example could you write...:

1.) A
2.) C
3.) E

etc rather than

1.) Amy
2.) Charlie
3.) Elliot

because writing it out in full would be a waste of time but then i dont want to run the risk of dropping any marks :/

Thanks but how did activity N become 2 days , dont quite follow that please

Yes that is fine. or you can use numbers such as reject 1-3 ,

when you are doing doing a binary search for names, it is important to write out the full names of the people involved? for example could you write...:

1.) A
2.) C
3.) E

etc rather than

1.) Amy
2.) Charlie
3.) Elliot

because writing it out in full would be a waste of time but then i dont want to run the risk of dropping any marks :/

I'm resitting D1 from last year.. but still don't understand linear programming at all! Its probably easy but i can't get my head round it at all.. how do you find out where they objective line is if you use that method? in the mark schemes they use specific points but i don't understand how to get them?
And also when you are asked to find interger optimal points how do you do that? Is it just from looking at the graph?
Thanks!
Good luck in the exam everyone!

I'm resitting D1 from last year.. but still don't understand linear programming at all! Its probably easy but i can't get my head round it at all.. how do you find out where they objective line is if you use that method? in the mark schemes they use specific points but i don't understand how to get them?
And also when you are asked to find interger optimal points how do you do that? Is it just from looking at the graph?
Thanks!
Good luck in the exam everyone!

When you have the objective function make it equal to something appropriate so it can be drawn onto your graph the reason you can choose what it's equal to, is because you only want the gradient

Say you have 3x + 2y

and your scale goes in 10s' all the way up to 50 on the x & y axis
You could go for 60 which is a nice number to choose

x=20 & y=30

mark those on the axis and draw a line through em, you have your objective line. Align your rule with this and more it across:

The first point your rule touches is the minimum point, it's possible to read this off the graph, but usually you have to do simultaneous equations to find the points co-ordinates.

The latest point your ruler touches is the maximum point

For interger value - it's again possible to see why is in the feasible region. But you can test various points you have and put them in your 2 inequality equations to see if they make sense.

So say I am testing x=2.4 & y=6.2 ... in the inequalities:
2x + y < 0 & 0< x + y

Though the second one gives me 0<8.6, the first inequality gives me 15<0 ..which obviously doesn't make sense, therefore the point is not in the feasible region and so on.....

I find this tedious and so long... so I hope we don't have to resort to this method in the exam

Oh sorry it will only reduce the project by 1 day, since it's critical path.....

.... so all other days being reduced is pointless, because it's not reducing overall project time

I don't think we should worry about the kind of Solomon Questions in all honesty

The Linear programming one was worse though, in our spec does it suggest we will always get linear programming question with only 2 variables? (as apposed to 3 x,y,z we got in solomon B)