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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Geraer1)
Can I ask which paper is that one? Thanks!

let me know as well (Y)
2. (Original post by tazza ma razza)
let me know as well (Y)
13R
3. (Original post by Ayman!)
13R.
Okay thanks!
4. Does anyone have a link for the S3 June 2015 exam ?
5. (Original post by SeanFM)
Ohhh, of course, sorry, there is another key difference - I see what you were asking now.

a) asks for the distribution of the orchids themselves, not the distribution of the mean of them.

So you use that a population is distributed ~N(20.1,0.5^2) for a) and a mean of n samples is distributed ~N(20.1, 0.5^2/n) for b).
ye i thought it was something to do with question a not mentioning the mean, is it basically n=1 for the orchids (not the mean)?
6. (Original post by tazza ma razza)
is a discrete uniform basically a pdf?
No. Discrete distributions have pmf's. Continuous distributions have pdf's.

(Original post by Armpits)
For goodness of fit tests, say you have a binomial distribution, do you work out the parameter p by default? Or do you just assume it. E.g. in an event with two outcomes, do you assume p is 0.5, or calculate it from observed data? I calculated in one q and lost some marks as it was supposed to be assumed.
The question will tell you. If they ask you to test test whether B(n, p) is a good model or not, you assume it. If they've asked you to calculate it in the previous part, then you calculate it.
7. (Original post by gagafacea1)
Zacken

Way to go Edexcel, loving the consistency.

(Original post by 20052009)
Does anyone have a link for the S3 June 2015 exam ?
Edexcel website.

(seriously the 10th time I'm having to say this...)
8. (Original post by connorbarr)
ye i thought it was something to do with question a not mentioning the mean, is it basically n=1 for the orchids (not the mean)?
I suppose you can think of it as taking a sample of 1 (hence n=1) so yes

(Original post by Zacken)
Way to go Edexcel, loving the consistency.

Edexcel website.

(seriously the 10th time I'm having to say this...)

Apologies - I will put it in a massive font in the OP.
9. (Original post by SeanFM)
I suppose you can think of it as taking a sample of 1 (hence n=1) so yes

Apologies - I will put it in a massive font in the OP.
10. (Original post by SeanFM)
Apologies - I will put it in a massive font in the OP.
Love it. I expect now I'll be saying "See OP."
11. (Original post by Zacken)
Love it. I expect now I'll be saying "See OP."
A lot shorter, I suppose

Thanks for the effort - it can be frustrating.
12. burning question guys:

ex3D q8a, why dont you use continuity correction - arent you going from poisson to normal?!?
13. (Original post by SeanFM)
A lot shorter, I suppose

Thanks for the effort - it can be frustrating.
I agree.

Right back at you! You seem to deal with it much better though. How'd your uni exams go?
14. (Original post by AakashG)
burning question guys:

ex3D q8a, why dont you use continuity correction - arent you going from poisson to normal?!?
No, you are using the CLT which states that the sample mean is normally distributed without continuity corrects no matter what the underling population distribution is.
15. (Original post by Zacken)
No, you are using the CLT which states that the sample mean is normally distributed without continuity corrects no matter what the underling population distribution is.
okay agreed! but then the red box on p37 - what and when is that relevant?

AND also looking at it now, why do you even need to use CLT for that question for part a? cant you just scale up poission mean and work out probability s2 style?
16. (Original post by AakashG)
okay agreed! but then the red box on p37 - what and when is that relevant?
It's not relevant.

AND also looking at it now, why do you even need to use CLT for that question for part a? cant you just scale up poission mean and work out probability s2 style?
No, just because the population is distribution poisson doesn't mean the sample mean is as well.
17. (Original post by Zacken)
I agree.

Right back at you! You seem to deal with it much better though. How'd your uni exams go?
Oh, no no no you take a lot more on than anyone else and kudos to you - it can be fairly draining when you see similar/the same questions being asked by different people, it's like they come and go but you're always there and it's not an easy thing to do.

Mixed bag, we shall see but the summer is now mine to enjoy.

I see you have Physics/FPs next month - feeling prepared?
18. (Original post by Zacken)
It's not relevant.
not relevant to this question or not relevant to s3?

(Original post by Zacken)
No, just because the population is distribution poisson doesn't mean the sample mean is as well.
this was my logic:

- mean is 2 per minute
- mean is 10 per 5 minutes
- mean is 300 per 5 minutes for 30 days <- or can you not scale up like that because its different days combined?

also, im still really confused, 8b) isnt that a basic poisson question, like why do we need to use CLT?

really appreciate the help!
19. Question: for the hypotheses in Spearman's rank questions, should you write them in both words and in terms of rho? E.g. "There is no association between the two variables (rho = 0)"

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