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# D1 (Decision 1) 17 May 2013 Official Thread Watch

1. (Original post by Westeros)
THE EXAM IS TOMORROW AHHHH! I'm really confident though, let's get top marks!
Good luck to you m'dear
2. (Original post by lizz-ie)
When do dummy variables need to be used?
Dummy variable? I don't recognise that phrase. Are you referring to a "dummy" arc when doing critical path analysis? In which case it is used to show precedence where it would not be possible otherwise. Eg if tasks X and Y both rely on A, however task Y also relies on B. A would connect into X and B would connect into Y, and then a dummy would come out of the end of A to the beginning of Y.

(Original post by study beats)
ALRIGHT SERIOUS QUESTION GUYS....

HOW DO U DO QUESTIONS LIKE WHEN THEY TELL YOU TO FIND WHAT ACTIVITIES ARE HAPPENING ON MIDDAY AT A PARTICULAR DAY USING UR GANTT CHART?

ALSO HOW DO U DETERMINE IF THE PROJECT CAN BE COMPLETED ON TIME ?

How do u use cascade gantt chart to determine the lower bound of workers needed ?
Look at your chart, and see what activities absolutely have to go through that time. You may be able to move around some activities within their float to get them out of the way. Conversely you may be asked what activites can be happening at a certain time, in which case you move them about in their float in order to pass through.

You can find a lower bound for workers by looking at a Gantt chart be seeing what the maximum number of activities are that ever have to be going on at one time. If that many activties need to be done at once, you need at least that many workers.

(Original post by Converse girl)
how do you find the optimal number and profit on a linear programing graph?
I use an objective line to find the maximum profit. Say you have P = 3x + 5 y. Change that to y = (3/5)x+C/5 and draw the objective line on your graph. You should clearly be able to see the vertex of your region with the maximum profit by imagining the line shifting up the graph (or down the graph if you wanna minimise your objective). Fin the coords of the intersection by simultaneous equations and smack those numbers into P.
3. (Original post by posthumus)
I think you'll be just fine surely you haven't forgotten much, I think you'd just want to get through the definitions! But don't pressurize yourself too much.

And a B is very good, which obviously suggests you have the potential to get an A and you know you can...
Some people will just never do well in D1, I know people who get like over 90 UMS but end up with Es in D1 ! Also I got 50 UMS in January
I got my paper back and compared it with the markscheme, and should've got another 7 marks. Which would've made it a high A, so as you can understand I was annoyed :P
I know someone who got a U in D1 but gets As in Core, so you didn't do that bad :P
Anyway, I've given up with Maths now, but good luck for tomorrow
4. How would you find the optimal solution if the line has a strict inequality ie < or >
5. (Original post by lizz-ie)
I got my paper back and compared it with the markscheme, and should've got another 7 marks. Which would've made it a high A, so as you can understand I was annoyed :P
I know someone who got a U in D1 but gets As in Core, so you didn't do that bad :P
Anyway, I've given up with Maths now, but good luck for tomorrow
aha, I'm sure you haven't given up really well if you have, then don't!!

Best of Luck with your 2 exams tomorrow
6. (Original post by Anythingoo1)
Good luck to you m'dear
Good luck to you too! I'm sure we'll be fine. Do we have to wait 12 hours or what not to discuss it?
7. (Original post by study beats)
ALRIGHT SERIOUS QUESTION GUYS....

HOW DO U DO QUESTIONS LIKE WHEN THEY TELL YOU TO FIND WHAT ACTIVITIES ARE HAPPENING ON MIDDAY AT A PARTICULAR DAY USING UR GANTT CHART?

ALSO HOW DO U DETERMINE IF THE PROJECT CAN BE COMPLETED ON TIME ?

How do u use cascade gantt chart to determine the lower bound of workers needed ?
Think about it midday is theoretically the middle of the day. Lets say you had a gantt chart the time of day when you reach that day is midnight. and midday is the middle then midnight again so it's in the middle of the day. Draw a line directly down and whichever one it cuts into has to be happening. Now check to see if you can clear it all the way e.g. move it to the late time and if it still cuts then it must be happening,
8. (Original post by lijojohn08)
How would you find the optimal solution if the line has a strict inequality ie < or >
Good point, no ones actually discussed this, it would obviously have to be within the region so I guess you will use testing

Get points that are around the point you found And see which ones are within the feasible region.

Though I highly doubt they would give such a question though as it's very long!
9. (Original post by Westeros)
Good luck to you too! I'm sure we'll be fine. Do we have to wait 12 hours or what not to discuss it?
It's at 9:30am so expect to discuss around 11pm / 12am.
10. (Original post by posthumus)
Good point, no ones actually discussed this, it would obviously have to be within the region so I guess you will use testing

Get points that are around the point you found And see which ones are within the feasible region.

Though I highly doubt they would give such a question though as it's very long!
Hi buddy

what does he mean?
11. has anyone got any tips on how to be as accurate as possible and avoid clumsy mistakes??
12. (Original post by otrivine)
Hi buddy

what does he mean?
when it's for example < rather than =<

therefore the variables you find on the line, are not valid.
You have to draw a dotted line for this... I would be surprised if it came up
13. (Original post by sarahjames123)
has anyone got any tips on how to be as accurate as possible and avoid clumsy mistakes??
The only way I learnt (from January) was that you actually need practice. I did no past papers, but this time I have done a couple and I feel much more prepared

Just stay calm and don't stress yourself too much, then you will not make mistakes (especially silly ones).
14. (Original post by posthumus)
Good point, no ones actually discussed this, it would obviously have to be within the region so I guess you will use testing

Get points that are around the point you found And see which ones are within the feasible region.

Though I highly doubt they would give such a question though as it's very long!
Thank you so much good luck
15. (Original post by posthumus)
when it's for example < rather than =<

therefore the variables you find on the line, are not valid.
You have to draw a dotted line for this... I would be surprised if it came up
But in all the papers and questions and questions from book everyting is with <= or >=

if they do < or > will the method be the same but to get the optimal you have to make sure it meets the requirments of the inequalities right
16. anyone any good tips for the exam?
17. (Original post by posthumus)
aha, I'm sure you haven't given up really well if you have, then don't!!

Best of Luck with your 2 exams tomorrow
By given up, I mean I've given up for tonight :P
Thank you, I hope your retake goes better than the first one
18. (Original post by otrivine)
But in all the papers and questions and questions from book everyting is with <= or >=

if they do < or > will the method be the same but to get the optimal you have to make sure it meets the requirments of the inequalities right
Not the same method, it's very long winded... look in the book. But I don't think it will come up and it never has, for a reason
19. (Original post by posthumus)
Not the same method, it's very long winded... look in the book. But I don't think it will come up and it never has, for a reason
20. (Original post by Zzzyax)
anyone any good tips for the exam?
Take your time and write all your steps clearly. Leave spaces inbetween lines so you can make corrections later

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