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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Zacken)
Seems a bit bleh, but I suppose it might just be examinable but, y'know, not actually going to be asked it in the exam, I haven't really seen 'proofs' in the S3 past papers before.
Thanks hoping for no proofs!
2. (Original post by economicss)
Hi, does anyone know please whether we could be asked to prove example 7 in the exam? Thanks Attachment 528137
I was asked to prove that in an exam last semester as part 1 of a question.

I think what you need to do there is to just understand the proof rather than memorise it, and be able to apply to anything reasonable.
3. Can someone explain why in quota sampling the size of the number in each quota do not have to be the same?

Is it just a first come first allocation basis?
4. (Original post by L'Evil Wolf)
Can someone explain why in quota sampling the size of the number in each quota do not have to be the same?

Is it just a first come first allocation basis?
Hmm? It's similar to stratified sampling, you want a certain proportion of each group.
5. In the S3 book on page 16, the sum of the quotas in each strata do not add up to the same number, idk if you have the book spare - I will try and upload. Thank you for the reply.
6. What is the differencce between spearman's rank and pearsons rank are they not both the same thing?
7. (Original post by L'Evil Wolf)
What is the differencce between spearman's rank and pearsons rank are they not both the same thing?
I believe the difference and when to use which one is explained in the textbook.
8. (Original post by L'Evil Wolf)
also which papers do people consider the hardest - would like to use them as mock papers.

And are the solomon press papers worth doing
2015 without a doubt, royally **** on me. then perhaps jan 09

yh i am doing solomon atm, about to start paper B.
9. (Original post by Rkai01)
x
10. (Original post by tazza ma razza)
2015 without a doubt, royally **** on me. then perhaps jan 09

yh i am doing solomon atm, about to start paper B.
that question 6 rip

Thanks will do them, q1 and q2 of 2015 were decent. But there was the 5 marker on the ND which I didn't square or something lmao.
11. (Original post by L'Evil Wolf)
that question 6 rip

Thanks will do them, q1 and q2 of 2015 were decent. But there was the 5 marker on the ND which I didn't square or something lmao.

ND? but yh, it started easy then sh1ts on you real quick
12. (Original post by tazza ma razza)
ND? but yh, it started easy then sh1ts on you real quick
normal distribution
13. In chapter 5 when there are tied ranks do we instead use that Sxx Sxy formula instead?
14. (Original post by SeanFM)
Oh my bad I thought I deleted my comment don't know why it says I wrote a x.
15. (Original post by Rkai01)
Oh my bad I thought I deleted my comment don't know why it says I wrote a x.
I wrote that x (it's a common letter used to quote someone, you can't leave the quote box empty) and I could not quote your post as you deleted it, but I saw it so.. there
16. (Original post by tazza ma razza)
2015 without a doubt, royally **** on me. then perhaps jan 09

yh i am doing solomon atm, about to start paper B.
There isn't a Jan 09 paper though?
17. (Original post by Rkai01)
There isn't a Jan 09 paper though?
Shout, looked at the wrong column of my scores sheet - try June 09 or June 04
18. For June 2013 4b. Why do we not take the variance as 6.88/50 rather than just 6.88? I'm sure I'd seen previously that we divide by n even if we estimate the variance. Thanks
19. (Original post by Rkai01)
For June 2013 4b. Why do we not take the variance as 6.88/50 rather than just 6.88? I'm sure I'd seen previously that we divide by n even if we estimate the variance. Thanks
No? The sample variance is given by ((sum of x^2) - n * (mean)^2)/(n-1) and that's that.
20. (Original post by Zacken)
No? The sample variance is given by ((sum of x^2) - n * (mean)^2)/(n-1) and that's that.
So say if in the next part it involved 100 people we would times the probabiltes by 100.
So there is no scenario where we'd need to alter the estimated s.d?

Okay say if we were given a normal distribution (we don't need to calculate anything) at the start of q4 would we then divide by 50 I guess as it involves 50 people?

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