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# Edexcel Mathematics S3 23rd May 2018 - Unofficial Mark Scheme & Discussion watch

• View Poll Results: How many marks do you think you got?
72-75
33.56%
68-71
21.70%
64-67
8.72%
60-63
7.83%
55-59
2.91%
50-54
6.49%
40-49
6.94%
30-39
4.47%
29 or less
7.38%

Things for copy/pasting: Chi2 H0: H1: X2 μ ρ Σ σ ≤ ≥ x̄ ȳ

1)
a) r=0.549
b) n=8, 5% CV: 0.6215, reject H1 - no evidence of positive correlation.
c) rs=0.714
d) n=8, 5% CV: 0.6429, accept H1- evidence of positive correlation.
e) Positive correlation between ranks but not linear.

2)
a) Explain stratified sampling, just in terms of letters/general examples not numbers.
b) H0: μps+6, H1: μps+6
5%CV = 1.6449
z=1.1888 < 1.6449, reject H1 + context statement
c) No need to assume since CLT guarantees the sample means are approximately normally distributed with a large enough sample size.

3)
a) x̄=1.55, s2=0.05667
b) P( | x̄ - μ | < 0.1) ≥ 0.99
z value for 0.5% (either tail) ≥ 2.5758
((μ+0.1) - μ) / (0.5/sqrt(n)) ≥ 2.5758
0.1 / (0.5/sqrt(n)) ≥ 2.5758
sqrt(n) ≥ 12.879
n ≥ 165.87
Minimum n=166

4)
a) k=0.47
b) 10% significance
H0: μ=6, H1: μ≠6
μ in confidence interval, not significant, accept H0, evidence for μ=6
c) σ=3.3741

5) Using a calculator
a) P(L - 3C > 0)
P=0.42015
b) P(C1+...+C8 + L1+L2+L3 > 20,000)
P=0.0033861
c) Assume they are independent (possibly also random and taken from the assumed distribution)

6)
a) H0: C~B(4, 0.5) is a good model for these data, H1: C~B(4, 0.5) is a bad model for these data
5 cells - 1 constraint = 4 degrees of freedom
CV 1% Chi2 = 13.2767, X2 = 17.52, greater than CV, Reject H0 + context statement
b) p=0.51
c) d=56.21 e=10.14
d) H0: The Binomial distribution is a good model for these data, H1: The Binomial distribution is a bad model for these data
e) 5 cells - 2 constraints = 3 degrees of freedom
CV 1% Chi2 = 11.3449
John should conclude his claim is wrong, as 16.9 was greater than the CV.
2. Hows everyone feeling, i find s3 pretty easy, just grade boundaries are annoying
3. (Original post by Competence)
Hows everyone feeling, i find s3 pretty easy, just grade boundaries are annoying
I feel the same way, I can reliably get about 70 (usually fall down on definitions, all the actual stats is fine) but that's only just, or not quite, an A* most of the time - it would be great to get 95+UMS 🤞🤞
4. Beautiful thread. Thank you for setting it all up in a nice manner.

Does anyone want to form a quick revision group right before the exam?
5. (Original post by plklupu)
I feel the same way, I can reliably get about 70 (usually fall down on definitions, all the actual stats is fine) but that's only just, or not quite, an A* most of the time - it would be great to get 95+UMS 🤞🤞
Same tbh i need about 97-100 UMS because my fp2 and m2 is looking shocking right now
6. (Original post by Competence)
Same tbh i need about 97-100 UMS because my fp2 and m2 is looking shocking right now
Me too! I figure if my S3 and S2 resit are ~95 each, I only need low 80s in M2 or FP2 for the A* (270 UMS in 3 A2 modules, I'm pretty sure), and I don't think I'll be getting any higher than 85 in either :/
7. Guys, I've made a last minute revision group - sensible use only please!

Feel free to send screenshots of any hard questions you come across

chat.whatsapp.com/3jKRM2twqx5LYUdZ04CVso
8. (Original post by Chittesh14)
Beautiful thread. Thank you for setting it all up in a nice manner.

Does anyone want to form a quick revision group right before the exam?
Nobody in the group yet, but please do share with anyone who is sitting the S3 exam. Feel free to send screenshots of any hard questions you come across

Sensible use only!

chat.whatsapp.com/3jKRM2twqx5LYUdZ04CVso
9. Good luck everyone!
10. Does anyone else find the IAL papers slightly different and harder?
11. (Original post by examstudy)
Does anyone else find the IAL papers slightly different and harder?
A little bit harder, but not by much. I did the 2014-2016 IALs recently, and I got the same scores as usual, around 73.
12. (Original post by Jono-Wolf)
Good luck everyone!
You too!
13. Wow thats really good, well done.
I definitely find especially the last questions quite different...

(Original post by plklupu)
A little bit harder, but not by much. I did the 2014-2016 IALs recently, and I got the same scores as usual, around 73.
14. (Original post by examstudy)
Wow thats really good, well done.
I definitely find especially the last questions quite different...
Thank you! I've been practising S3 for a while, it's the module I'm most proud of.

I think they stopped doing January exams a few years ago.
15. (Original post by plklupu)
Thank you! I've been practising S3 for a while, it's the module I'm most proud of.

I think they stopped doing January exams a few years ago.
Whoops! you can probably tell I haven't
16. (Original post by examstudy)
Whoops! you can probably tell I haven't
Haha, I'm sure we'll all smash it regardless
17. (Original post by plklupu)
Haha, I'm sure we'll all smash it regardless
sucks we are all competing against each other for grade boundaries but good luck everyone hopefully edexcel chills with grade boundaries
18. (Original post by Competence)
sucks we are all competing against each other for grade boundaries but good luck everyone hopefully edexcel chills with grade boundaries
Edexcel are never chill with S3, get ready for 70/71 raw -> 90 UMS
19. https://i.imgur.com/eOGGzWr.jpg
quick question do I have to add the sum oi^2/Ei
row to gain marks or can I just leave it and just calculate directly. will I still get the marks?
20. (Original post by assassinbunny123)
https://i.imgur.com/eOGGzWr.jpg
quick question do I have to add the sum oi^2/Ei
row to gain marks or can I just leave it and just calculate directly. will I still get the marks?
Show yourself adding it together, it does gain you a couple marks i think.

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