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# OCR S2 (non-mei) watch

1. (Original post by jacobe)
I literally got everything that you got!
I'll take that as a good thing! I'm not usually one to post my answers on here but I'm fairly confident that they're right. It took me ages to understand what to do for 8ii) so it's good to see that others agree with me
2. For question 7, if you did use n=38 and actually carried out the test, you ended up accepting H0, and I thought you were sposed to be finding the max value so that you still rejected H0?
So shouldn't n by 37?
3. Basically you'd get 38 if you put P(X<x) and 37 if you put P(X≤x) but I mean your point of poisson makes sense :/
4. But I mean, without any approximation
x~Po(50)
P(X≤38) = 0.04737 < 0.05
Soooooo, i wanna believe they will allow 38 (because q4 and 8ii screwed me over, i need every mark i can get)
5. will I lose marks for putting down the exact answer, and then rounding to 3sf for every question? Thanks
6. (Original post by gothmog827)
will I lose marks for putting down the exact answer, and then rounding to 3sf for every question? Thanks
No that's what you're supposed to do, as instructed on the front cover, to leave answers rounded to 3sf unless another degree of accuracy is asked for or clearly appropriate
7. Whats been the highest grade A boundary for S2 ? Thnx
8. For 7 was it 0.1247>0.05 so accept Ho.

I got that by doing x-Po(5) for 15 days, then doing the probability x was less than or equal to 2 which was 0.1247. Did anyone else get this?
9. (Original post by Qwerty1996)
For 7 was it 0.1247>0.05 so accept Ho.

I got that by doing x-Po(5) for 15 days, then doing the probability x was less than or equal to 2 which was 0.1247. Did anyone else get this?
Sounds familiar
10. (Original post by jaymf10)
Whats been the highest grade A boundary for S2 ? Thnx
I think it was 67 for an A*, the highest yet.

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11. Yes
12. Basically.... I think u forgot cc of 0.5...should be 37 G
(Original post by randomnes)
I remember it being like 38.48 (above 38) so the answer for the highest point failures was 38
13. (Original post by ferdy118)
Numerical answers I got (in order of appearance and also includes values used of probabilities I used to determine whether to reject the null hypothesis in hypothesis testing).
Question 1: 2 and 146
2iii) 0.222
3i) 6
3ii) 1.5
4: 0.8311 and then 0.2536
5. 0.0569 (do not reject)
6. 0.0249 (for the 11-marker and I rejected Ho)
7i) 0.1236 (do not reject Ho)
7ii) 37
8i) 3.15%
8ii) 0.653
Let me know if you agree!
For 7i) How did you get 0.1236? I got 0.1247 but I could definitely be wrong
14. You're right and I got that answer too haha, I'd saved all my answers in my calculator but I didn't quite know what questions they corresponded to. It was a Poisson distribution with it being an average of 1 points fault for every 3 days. So over 15 days Ho is 5 points faults. The engineers had reduced this to 2 points faults so P ( X ≤ 2) = 0.1247.
(Original post by Qwerty1996)
For 7i) How did you get 0.1236? I got 0.1247 but I could definitely be wrong
15. Basically... I said "x is any particular outcome of X"... U think il get the mark???
16. (Original post by lllllllllll)
For Q7 I think 41 may be the answer for 7(ii). I've put the solution below I case anyone wants to double-check/verify?

1 out of every 3 trains are late
Therefore 1/3 out of every 1 train is late, so p = 1/3 and n=150 (from the question)

Let X distribute binomially

approx.

Your big mistake is that you've assumed it's a Binomial distribution. We're told in the question it's Poisson. By using Binomial, you're (incorrectly) assuming that you can only have one points failure per day.

It should be a Po(50) distribution, which you can approximate by N(50,50). A correct continuity correction gives an exact n of 37.87, so the answer is 37.

(You've also made the wrong continuity correction, so you won't get that mark either; I'm guessing you might get 1 out of 6 marks overall)
17. (Original post by Mr M (jr))
Your big mistake is that you've assumed it's a Binomial distribution. We're told in the question it's Poisson. By using Binomial, you're (incorrectly) assuming that you can only have one points failure per day.

It should be a Po(50) distribution, which you can approximate by N(50,50). A correct continuity correction gives an exact n of 37.87, so the answer is 37.

(You've also made the wrong continuity correction, so you won't get that mark either; I'm guessing you might get 1 out of 6 marks overall)
I think I've dropped 7 marks on this module now. Mainly because of this question what do you think the grade boundaries will be?

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18. (Original post by lllllllllll)
I think I've dropped 7 marks on this module now. Mainly because of this question what do you think the grade boundaries will be?

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I don't guess grade boundaries. What I will say is that it seemed quite a "fair" paper; not the easiest S2 paper ever, but not the hardest. The average for an A in S2 has been 58; the average for A* has been 65.
19. (Original post by Mr M (jr))
I don't guess grade boundaries. What I will say is that it seemed quite a "fair" paper; not the easiest S2 paper ever, but not the hardest. The average for an A in S2 has been 58; the average for A* has been 65.
Thanks I guess I'll end up somewhere on the boundary for S2

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20. (Original post by lllllllllll)
Thanks I guess I'll end up somewhere on the boundary for S2

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Basically last yearin S2 you could drop 6 for 90 UMS... It will probs be the same this year.... So just take worst case scenario and smash FP2 xx..... Also what does everyone think about D2 boundaries.... You feel they will be the same as last year 64/72 for 90ums??

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