# S2 exam official threadWatch

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14 years ago
#21
I was the only one in the whole hall Got very lonely and cold. Don't want to say how I found it because it always jinxes my result...hehe
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14 years ago
#22
(Original post by MdSalih)
Yep.. Edexcel.. personally found the paper very good - am happy with it - had 30 mins left for question 7 at the end

My recollection of exam:

1)a) Given R~B(15,0.3) -- find P(R=5) ... 0.2061 (2)
1)b) Given S~Po(7.5) -- find P(S=5) ... 0.1094 (1)
a)c) Given T~N(8,2^2) -- find P(T=5) ... 0 (1)

2)a)i) What is a population
2)a)ii) What is a Sample Frame (2)

2)b) Explain why sample frame != population (1)
2)c) Give an example with reason of Census & Sample(4)

3)a)Stick of length 2l is broken into two... define pdf of length of shorter half .
Uniform/Rectangular Distribution...
f(x) = 1/l for 0 < x < l // 0 otherwise
(3)

3)b) P(X< l/3)... 1/3 (2)
3)c) E(X) ...... l/2 (1)
3)d) P(Both broken sticks being of length l/3)... (1/9) (2)

4)a) Give two additional conditions of binomial (2)
4)b) Perform hypothesis test with 1% significance level.. I remember I ended up doing normal distribution... 1 - phi(3.06)... interpolated as it wasn't in table got 0.011 - insignificant result. (6)
4)c) Commet on assumption... think this had to do with the interpolation .. think your ment to comment on that.. not sure (2)

5)a) Defecient article has probability of 0.032 ... so find probability of exactly two articles being defficient out of 10 articles... 0.0355 (3)
5)b) Sample size increased to 100 ... as n is large p is small... use poisson... 0.6025 (4)
5)c) Sample size increased further to 1000... approximate to poisson first with mean 32.. then approximate to normal... eventually got answer of 0.0294 (6)

6)a) Accidents on a particular stretch of road had mean of 3 per month, evaluate probability of there being more than 4 in a month... 0.1847 (3)
6)b) Probability of there being more than 4 in 3 months (I think)... 0.945 (2)
6)c) Do hypothesis test with 5% significance level to see if need speed regulation measures have made an impact given only 1 accident per month nor on average... 0.1991 > 0.05 -- so not sigificant. (4)
6)d) Do hypothesis test with 5% to see if new speed regulation has had an affect given only 55 accidents in 2 years... 0.0262 < 0.05 - significant result. (7)

7)a) Show k = 2/9 (3)
7)b) Find E(X) ... 2.5 (3)
7)c) Find Mode(X) ... 2.5 (2)
7)d) Find the CDF...
F(X) = 0 for x < 1 // (1/27)*(-2x^3 + 15x^2 -24x + 11) for 1 <= x <= 4 // 1 for x > 4 (5)
7)e) P(X <= 2.5) 0.5 (2)
7)f) Deduce Median... and comment on distribution... m = 2.5 as F(2.5) = 0.5 .. distribution is symmetrical. (2)

Absolutely loved question seven.. cos you could see where it was going.. and you knew it was right when it said "deduce the median.. and comment on the distribution"

Marking scheme (given in red) should now be correct
[Edit2]Corrections made to Question 5 - thanks to the person who pointed them out.. don't know forum nick

MdSalih
I don't think your correct on question 4. For part b if you look up Ph of 3.06 its 0.9989 so 1-0.9989 is 0.0011 not 0.011. Hence result IS significant. Correct me if I'm wrong?
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Thread starter 14 years ago
#23
(Original post by dieeiervonsatan)
I don't think your correct on question 4. For part b if you look up Ph of 3.06 its 0.9989 so 1-0.9989 is 0.0011 not 0.011. Hence result IS significant. Correct me if I'm wrong?
Yeh you are right i think...that was the beans question werent it? 0.1 prob, 250 kids etc....40 guessed the difference. If thats the same question then it was sig and there was evidence to suggest the 10% claim was inncorrect!!
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14 years ago
#24
(Original post by dieeiervonsatan)
I don't think your correct on question 4. For part b if you look up Ph of 3.06 its 0.9989 so 1-0.9989 is 0.0011 not 0.011. Hence result IS significant. Correct me if I'm wrong?
yes it was 0.0011, but the significane leve was 1% wasnt it?
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14 years ago
#25
(Original post by Syncman)
yes it was 0.0011, but the significane leve was 1% wasnt it?
Yes, so 1% is 0.01 and since 0.0011<0.01 then the result is significant right?
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14 years ago
#26
I have a question.. have a bad feeling I rounded most answers to 3sf, is that bad? Or do they only accept 4sf ?
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Thread starter 14 years ago
#27
(Original post by dieeiervonsatan)
I have a question.. have a bad feeling I rounded most answers to 3sf, is that bad? Or do they only accept 4sf ?
On the old mark schemes they tended to accept 3 or 4 s.f, i just used 4 s.f...dont think it will matter too much though!
....& yes, 0.0011 < 0.01 so it is significant as it lies within the critical region.
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14 years ago
#28
(Original post by jmzcherry)
On the old mark schemes they tended to accept 3 or 4 s.f, i just used 4 s.f...dont think it will matter too much though!
....& yes, 0.0011 < 0.01 so it is significant as it lies within the critical region.
Hmm I'm kinda a bit worried about it, because I did one paper were I rounded everything to 3 s.f. and they didn't accept anything but 4.s.f. But I totally forgot that on the real thing!
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14 years ago
#29
(Original post by dieeiervonsatan)
Yes, so 1% is 0.01 and since 0.0011<0.01 then the result is significant right?
Oh poo!
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14 years ago
#30
i didnt take into account the fact it was the shorter section of the rod in q3 (i think) so got the wrong interval - hope there are sum follow through marks!
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14 years ago
#31
(Original post by jmzcherry)
Yeh you are right i think...that was the beans question werent it? 0.1 prob, 250 kids etc....40 guessed the difference. If thats the same question then it was sig and there was evidence to suggest the 10% claim was inncorrect!!
Yup correct.. silly me.. there goes two marks outta the window.. should get marks for working... /me crosses fingers :P

MdSalih
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14 years ago
#32
(Original post by Syncman)
Oh poo!
Hehe sorry!
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14 years ago
#33
(Original post by jmzcherry)
Just got back from my S2 exam, didnt find it too taxing so hopefully the UMS marks will come flying in! How did everyone else find it?
Really?

I thought that there was simply too much to do for Edexcel S2. I dropped around four marks due to running out of time.

John
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14 years ago
#34
(Original post by PhoenixSTL)
I was the only one in the whole hall Got very lonely and cold. Don't want to say how I found it because it always jinxes my result...hehe
There was some sort of GNVQ exam which finished before me, so I ended up alone too with the head of maths sat somewhere behind me.

John
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14 years ago
#35
(Original post by kevins)
got 95% first time round in june GO MEE!!
lol
I thought that the Edexcel S2 paper was dead easy in June. I spanked the paper, only to find that I got only a pathetic 53%!! I have had it remarked (no change) and getting it back did not make me understand the problem.

This time around I made sure that I showed far more workings. I hope to get over 80%, but you never know!

JP
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14 years ago
#36
(Original post by MdSalih)
Yep.. Edexcel.. personally found the paper very good - am happy with it - had 30 mins left for question 7 at the end

My recollection of exam:

1)a) Given R~B(15,0.3) -- find P(R=5) ... 0.2061 (2)
1)b) Given S~Po(7.5) -- find P(S=5) ... 0.1094 (1)
a)c) Given T~N(8,2^2) -- find P(T=5) ... 0 (1)

2)a)i) What is a population
2)a)ii) What is a Sample Frame (2)

2)b) Explain why sample frame != population (1)
2)c) Give an example with reason of Census & Sample(4)

MdSalih
For 1 (C), I put that the it was not possible to find the probablilty of a discrete number for a continuos distribution. Is this right?

Also, I had a guess for 2 (b). I wrote that the sample frame may not be up to date so the list may not have every member of the population. Reasonable?

JP
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14 years ago
#37
(Original post by dieeiervonsatan)
I have a question.. have a bad feeling I rounded most answers to 3sf, is that bad? Or do they only accept 4sf ?
I think that is fine.

I always show the full number, and then show it to 4dp.

JP
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14 years ago
#38
(Original post by John Porcella)
I thought that the Edexcel S2 paper was dead easy in June. I spanked the paper, only to find that I got only a pathetic 53%!! I have had it remarked (no change) and getting it back did not make me understand the problem.

This time around I made sure that I showed far more workings. I hope to get over 80%, but you never know!

JP
I did D1 last summer and i got a miserable D (50 UMS) only to have it remarked to 79 UMS

OCR - you screwballs
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14 years ago
#39
(Original post by manps)
I did D1 last summer and i got a miserable D (50 UMS) only to have it remarked to 79 UMS

OCR - you screwballs
That's shocking!
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