D1 (edexcel) today TOTALLY HARD

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Evil, evil paper.

The strange thing was I did loads of mocks and never found them difficult, always finishing like, 30-35 minutes early... and then I did that paper and almost ran out of time.

Questions:
1) Bipartite graph; not too shabby. Did a 1a 1b arrangement. Bit of a dodgy question since it was infact impossible to find a complete alternating path, it kept reaching dead ends, so after trying for 10 minutes you finally read the next bit of the question "oh by the way, it's actually impossible..." Stupid idiot examiners. Don't *think* I made any mistakes. But then this is D1.
2) Ah, a quicksort-binary search question. Yaay. Hurrah, hurrah :cool:

3) Chinese postman? Nice and easy except for part c) about which two vertices would you choose. I forgot that you would choose one of the pairs you had to do twice because then it becomes unnecessary. Blah.
4) Forget this question. CPA?
5) Flows. We hadn't been taught how to find backflow - so this was an interesting question for me. I only managed 2 augmenting routes - +8 and +1 resulting in 62. The rest of my college did the same, but you should see the examiner's report "some CENTRES were able to answer better than others" which doesn't give me a lot of confidence in my maths teacher. Better go over S2 by myself!
6) Linear programming. This sucked. I couldn't get all the inequalities - but STRANGELY I managed to come out with 400 100 being the best (x must be at least 20% of the total production) which gave me a profit of £190 - so they gotta give me credit for tryin, right? Maybe an A1 mark somewhere?! :biggrin:

7) Why can't I remember this question?! Help me out somebody!

-Dragon ShadowStorm

P.S. Way to break in the exam season. D1 was my first exam.

Reply 21

spongebobfan

hmm i got more zeros in my 190 pounds thing.. like 19000 lol... cos the profit equation.. wasnt it 30x + 40y or something? oh shite... well yeah and i got the 65 flow and cut tho at first i thought it would be something where id have to take one off and put it somewhere else etc and panicked.. also spent a while drawing supersource and supersink but crossed it out hmm dunno how smart that was...... oh and 38 for dijkstra? two paths, SCEsomething and SA..GT something like that.. aaandddd yes route inspection hehe i said the practical problem would be a postman how gay well yea and got 41 for the thing i have to repeat. two routes. also for workers i said 3 or 4 cos they didnt give a limit for how many workers OR the minimum time! I mean, for all you know, minimum time could be way up there like 100 days or minimum workers could be 10! So I put 3 or 4.. glad its only 2 marks and didnt have to draw up the schedule. how many marks was cascade? and the first question? why you cant get a complete matching? ahhh so screwed uppp.... hmm if the grade boundaries are so low then i might as well just leave it to them lol oh but i really needed 100 in this paper... oh wellz i'll redo it next year and hopefully that one will be easier. :smile:

Reply 22

username9303

Yer that paper was quite tricky, timewise it werent good :frown:

My views:

1) not a problem once i realised why there were 6 dots on the right

2) got 37 mins for the dijsktras and then 39 mins when they added the extra condition that it went through C

3) did the route inspection algorithm and got a total length of 299

4) used quick sort and then binary was ok

5) x=9, y=16, initial flow = 53. Got 64 as the maximum flow because as someone posted earlier, the minimum cut was 64. their diagram was awful, it was so hard to understand

6) got £190 as the profit, with x=100 and y=400

7) gantt charts were annoying as eva, takin ages to draw out properly - got 25 as the length of the critical path, with B,C,E,F,I,J,L as the critical activities, with 4 workers needed.

Anyone like to correct my answers on any of those? Would be most grateful, ollie.

Reply 23

SsEe

I think I only got 3 workers required. I totalled the time of all activities up and divided by 25 giving 2.xxx therefore 3 would be the theoretical minimum. But two people have said 4 now so I've more than likely mucked up. Probably missed adding on an activity or three to the total.
And for the 19000 answer. That's becuase the question was set in pence so the answer was also in pence. People just put £190 instead.

Reply 24

username9303

yer ur right about the 19000 pence thing. i added all the lengths up and divided by 25 like u said, and got 2.xxx and so i wrote 3 workers. but when u checked back on the Gantt chart, there were 4 things that had to run at the same time, because of the two critical paths and two other activities having insufficient float to put together, so it needed 4 workers.

Had anyone actually conferred with their teacher about whether the maximum flow is 64 or 65? Because at my school it was a 50-50 split of people going each way.

Reply 25

squigglybob

Damn that stupid flow problem!! :mad:

Why did they have to put on those stupid little arrows on for us!

That just made me mad and lost me 5 mins or so (crucial seeing as there was hardly any time for the exam!!! :mad:

0)

In the end i just crossed out their ones (which were in the wrong directions to how i usually have them grrrr) and drew my own.

So sucks to those stupid time saving exam scripters!!!!!

All sorted tho!

Yo ollie! and im afraid SsEe that ollies right about the four workers i got exactly that as well.

As for that minimum cut i cant remember whether it added up to 64 or 65, but i do know that i had all the paths saturated long my min cut (except for that one that went the wrong way lol)

I cant believe they didnt have a simplex (rant rave) :mad: