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Ocr mei decision 1 maths exam -- 6th june 2013

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How I found it:

Graph Theory (1) last part - where it asks you to repeat the process for a different map. I wasn't quite sure if the second graph you had to draw was planar like the first bit - I didn't in the end and crossed arcs.

Algorithms (2) - This didn't seem TOO bad to me, long as you understood what it was asking before you ploughed on ahead trying to complete it. Basically, it was a bubble-sort algorithm. I think there were 6 numbers needed to be sorted? Either way, I remember every pass I had to do had 2 swaps (except the last one, no swaps), so it resulted in 15 comparisons and 8 swaps in total.

Networks (3) - The application of Dijkstra's algorithm was fairly standard and straightforward I thought, and so was the analysis of the shortest routes. I did like the part about how to adapt the algorithm, I wonder if others thought about converting the 'distance' weights to 'time to travel'. About how to adapt the node C, I tried to describe inserting a complete network in that point to connect each junction with each other at C, each with a weight of 20 (minutes, or 1/3 hour). No idea if this was a wise thing to do...! :tongue:

Critical Path Analysis (4) - Oooh, i hate these. EVENTUALLY, I managed to draw an activty on arc diagram... Thankfully, the forward and backward pass seemed fairly simple, as was identifying critical activities. Thankfully no question on floats...! I found the earliest finish time to be 100 minutes. Oh, and I love cascade diagrams. That part also seemed average.

Linear Programming (5) - Skis (y) and snowboards (x). I never had to do this when I went to Austria, that's for sure. The relationships themselves weren't that bad, I remember x+y≤600 and 1.1y≥x, along with x≤350(?) and y≤500. The last half really got to me, however. I somehow found that it would have to be an increase over €10 to change the optimal point. I eventually got to two conflicting answers, and I plumped for what is now evident to be definitely wrong.

Simulation (6) - This was a bit tricky.. It seemed so simple at first, use a few rules to figure out a few times per person and do 10 simulations. The bits that required thought: Having a cumulative arrival time table, because the values you were simulating were the time intervals between people arriving; then the last but one part where you have to consider waiting times for the two events (shopping(?) bit and the paying bit), and having to add times on and carry them through; The last part seemed a bit empty to me, I only had one action to take in my simulation. Probably made a few slips here and there.

All in all, blegh. Thank god I can now stick to purity and mechanics. S2 was a nice relief to have after that. :smile:

Grade Boundaries? D1 usually tends to be quite low - I don't think this one will be different.

(edited 10 years ago)

Reply 61

JackVM

Original post by Monotypical

So has anyone got an answer for iii)? I put it as 6 euros per snowboard but I see now that I misinterpreted the question, and even that's wrong then

I got it to be 7.14 Euros, but in hindsight I think that's wrong
It's the price the snowboards would need to be so that a new intercept on the graph would be used, which would occur when the gradient of the profit function is equal to that of the 1.1y>x one.

Reply 62

Monotypical

Original post by JackVM

Now that I look at it, it's not how much extra he would have to charge per snowboard, it's how much extra would he have to make overall, which I guess would be 29000 - (the next nearest value) which I think is around 1000?

Reply 63

Monotypical

Original post by Political Cake

Networks (3) - The application of Dijkstra's algorithm was fairly standard and straightforward I thought, and so was the analysis of the shortest routes. I did like the part about how to adapt the algorithm, I wonder if others thought about converting the 'distance' weights to 'time to travel'. About how to adapt the node C, I tried to describe inserting a complete network in that point to connect each junction with each other at C, each with a weight of 20 (minutes, or 1/3 hour). No idea if this was a wise thing to do...! :tongue:

I converted 20 minutes @ 30mph into the equivalent of an extra 10 miles, so all nodes connected to C must have 5 added to them, so when you go through C you travel the equivalent of an extra 10 miles, which is 20 mins @ 30mps

Reply 64

louci

Original post by JackVM

Yeah, I think so, I can't remember too great though

This was the hardest paper I've tried, I've never been so stressed in an exam

ahha lol same here ! that is a bit more reassuring ..we can only hope than ...that grade boundaires are low !

Reply 65

Waddsy

Original post by Monotypical

But I thought it was how much extra was charged per snowboard? I got 10 euros anyway.

Not sure about question 1ii found it hard to interpret what it meant by a map I just drew the same graph again pretty much. Found the rest of the paper ok once I realised the algorithm was bubble sort but my swaps may have been wrong as mine went 3,2,1,0 in corresponding rows. Since no-one has given their simulation end time yet did people get 19.75 for the first one with 19.25 for the second?

Reply 66

louci

Original post by Waddsy

i have to agree with ur simulation end time ..but my friends got different times .. i just assumed i got it wrong lol

Reply 67

smart_cookie

Hey guys! I did this paper too, and I have to say it was probably the the worse D1 paper to date! Seriously, you know your screwed if you can't even make sense of the first question! Did any anyone else feel really rushed for time, as in more than usual for a D1 paper?

Reply 68

Monotypical

Original post by Waddsy

Not sure about question 1ii found it hard to interpret what it meant by a map I just drew the same graph again pretty much. Found the rest of the paper ok once I realised the algorithm was bubble sort but my swaps may have been wrong as mine went 3,2,1,0 in corresponding rows. Since no-one has given their simulation end time yet did people get 19.75 for the first one with 19.25 for the second?

Original post by louci

i have to agree with ur simulation end time ..but my friends got different times .. i just assumed i got it wrong lol

I concurr.

(edited 10 years ago)

Reply 69

Monotypical

Original post by Waddsy

But I thought it was how much extra was charged per snowboard? I got 10 euros anyway.

Angelo considers increasing the cost of snowboard hire so that snowboard profits rise enough to change the optimal solution.
(iii) By how much will snowboard profits have to rise to change the optimal solution

Could be interpreted either way I guess, but it sure isn't 6 euros :frown:

Reply 70

yoyox120

I messed up the line with that 1.1y = x or w/e it was but I then moved on to do the rest correctly. Would I get error carried forwards? Seeing that this line determined how many more snowboards were worth keeping or something? I can't remember :s-smilie:

Reply 71

yoyox120

Original post by Monotypical

I do believe I got 100

I got 95 initially but realised I left activity L out and put it in to get 100.

Reply 72

Monotypical

Original post by yoyox120

You may lose 1 mark for an error in drawing a line, but seeing as you normally calculate where 2 lines meet, it doesn't matter how you draw them on your graph (as long as the right lines intersect)

Reply 73

Benstrat95

The price increase should have been €4.74 as the difference was €1500 euros, only selling 250 snowboards so to make up the difference. every snowboard needs to be increased by this price. The critical path analysis end time was 100. Very nice easy paper

Reply 74

Waddsy

Original post by Monotypical

Could be interpreted either way I guess, but it sure isn't 6 euros :frown:

Is that the question word for word because it probably is £1500 if it is

Reply 75

Monotypical

Original post by Waddsy

Is that the question word for word because it probably is £1500 if it is

Yeah, that was it word for word taken from the scan on page 3 of this thread

Reply 76

yoyox120

So could someone drop a comment on what the grade boundaries are likely to be? I did my D1 mock in college, it was the Jan 13 paper and I got 56/72 which was one mark off an A. I found that paper not so hard, but this I found horrible..

1. Messed up the algorithm and didn't do the last parts.... :/
2. Messed up an inequality in the LP question
3. Messed up on the simulation where I forgot to include waiting times >.<
4. Finally I didn't do the 2nd parts of the first graph theory question. I was so pressed for time :s-smilie:

Idk..Looking at it I probably got like 50-55 out of 72 :frown:

How low we expecting the boundaries to be?

EDIT: Why the negative rating...........just lol.

(edited 10 years ago)

Reply 77

Waddsy

Original post by Monotypical

Yeah, that was it word for word taken from the scan on page 3 of this thread

Seems like a fair few people made a mistake on that one thankfully it was only a one marker when it could of been at least 2

Reply 78

Political Cake

I found the price increase different:

Maximise 40x+50y

The optimal solution before was (100, 500) to have a profit of €29,000.

I then used another point, and found the difference in profit to be €1,500.
But I figured that if you increased the prices of snowboards, then the profit of the original point also increased. Eventually they joined at €30,000 (difference of €1,000) so I said that it required snowboards to be increased in price by (at least) €10 (to change the optimal solution)

Reply 79

Monotypical

Original post by Political Cake

thank you, that is what I was looking for, I put it down as 6 euros but I then realised that changed the 29,000 euro point aswell, thought I was going to have to do something with limits or w/e, but I only noticed about 2 minutes from the end when I was going over it :/