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Official Edexcel S3 thread Wednesday 20 May 2015 Morning [6691]

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Original post by 1 8 13 20 42
I'm not sure there are many good videos...from what I remember examsolutions has a couple but doesn't cover the majority of it yet. Why do you need videos? The textbook is pretty good.
edit: Scratch that on inspection I don't see any lol


Lol I cant find any either. :/
I'm self teaching it and just getting a few equations and 2 examples doesnt really help. I'm finding it hard to apply the equations to the context of the questions. If that makes sense
Original post by AyferBodur
Lol I cant find any either. :/
I'm self teaching it and just getting a few equations and 2 examples doesnt really help. I'm finding it hard to apply the equations to the context of the questions. If that makes sense


Shall we join forces and try and sort out S3 together? :wink:


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Original post by AyferBodur
Lol I cant find any either. :/
I'm self teaching it and just getting a few equations and 2 examples doesnt really help. I'm finding it hard to apply the equations to the context of the questions. If that makes sense


Original post by skyaviator23
Shall we join forces and try and sort out S3 together? :wink:


Posted from TSR Mobile


If you're stuck, feel free to post questions. It has been over a year since I've done S3, though :colondollar:

I don't have the textbook to hand so I'm not in a position to be able to explain concepts, but if you come across something and think 'what does this mean' then if you upload a photo of the relevant pages then I can try to help out. :smile:
(edited 8 years ago)
I'm thinking of doing some S3 videos at some point... will get back to you if I do. In the meantime feel free to ask me any questions about it. :ahee:

Posted from TSR Mobile
Original post by Krollo
I'm thinking of doing some S3 videos at some point... will get back to you if I do. In the meantime feel free to ask me any questions about it. :ahee:

Posted from TSR Mobile


Hi there, Could someone please explain the Central Limit theorem? From chapter 3
Original post by L.Yagami
Hi there, Could someone please explain the Central Limit theorem? From chapter 3


Sorry i never made those videos lol.

Anyway, without further ado, the central limit theorem:

Suppose you have ten pound coins, and flip each one. You'd expect to have somewhere in the range of five heads, yes? Indeed, if we say that H represents the number of heads, we could say that E(H) equals 5.

Let's take this slightly further. If you get to keep any of the coins that show a head, then the expected winnings from the flip of any individual coin is 50p - you have a 50-50 chance of winning the coin in each case. In other words, the expected mean of the winnings taken over all the coins is 50p. Let's say the winnings from the coin number i is Xi, with Xi = 1 if it shows a head, and Xi = 0 if it shows tails. Then the mean of Xi will be 0.5, however many coins you have.

However, if we go back to the original ten coins, sometimes you'll win £3, sometimes you'll win £7, sometimes you'll win £5 dead on. The central limit theorem can be used to estimate the chances that each of these instances happens.

The crux of the idea is that the mean of any variable - whether the variable itself is poisson, uniform, or whatever - is always normally distributed, with a mean equal to the mean of the original variable, and a standard deviation equal to the original s.d. divided by root(n), where n is the number of observations.

(I'll expand on this later, in a slight rush)
Hi, Please could someone explain to me how to do question 7d on this paper https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202011%20QP%20-%20S3%20Edexcel.pdf I would be really grateful :smile:
Thanks
Original post by economicss
Hi, Please could someone explain to me how to do question 7d on this paper https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202011%20QP%20-%20S3%20Edexcel.pdf I would be really grateful :smile:
Thanks


What is the distribution of xbar - mu?
Original post by SeanFM
What is the distribution of xbar - mu?


Yeah :smile:
Original post by economicss
Yeah :smile:


I'm asking you :tongue: it's not quite what the question is asking but it is definitely a way of doing it.

So what is it? :tongue:
Original post by SeanFM
I'm asking you :tongue: it's not quite what the question is asking but it is definitely a way of doing it.

So what is it? :tongue:


Whoops haha, erm the total of the weights divided by whatever the value of n is? :/
Original post by economicss
Whoops haha, erm the total of the weights divided by whatever the value of n is? :/


Not quite what I'm looking for. :redface:

Xbar is normally distributed with mean ... and variance ...

Therefore xbar - mu is ... distributed with mean ... and variance ...

and this helps you with the question as ....
Original post by SeanFM
Not quite what I'm looking for. :redface:

Xbar is normally distributed with mean ... and variance ...

Therefore xbar - mu is ... distributed with mean ... and variance ...

and this helps you with the question as ....


Sorry haha I'm so bad at stats, I'm guessing xbar-mu has mean 0 and variance 9 but I think that's wrong? Thanks!
Original post by economicss
Sorry haha I'm so bad at stats, I'm guessing xbar-mu has mean 0 and variance 9 but I think that's wrong? Thanks!


Half correct :borat: the mean is indeed 0.

Sorry that I'm drawing this out, but I'm trying to aid your understanding :tongue:

What is the distribution of just xbar of a sample with mean mu and variance sigma^2?
Original post by SeanFM
Half correct :borat: the mean is indeed 0.

Sorry that I'm drawing this out, but I'm trying to aid your understanding :tongue:

What is the distribution of just xbar of a sample with mean mu and variance sigma^2?


Progress at last! Thank you, I appreciate your help!! Erm it would have mean mu so in this case 0 and the variance would be sigma squared divided by n?
Original post by economicss
Progress at last! Thank you, I appreciate your help!! Erm it would have mean mu so in this case 0 and the variance would be sigma squared divided by n?


No worries :h:

Yes, that's correct.

So what distribution does xbar - mu have?

and then how does this help for the question?
Original post by SeanFM
No worries :h:

Yes, that's correct.

So what distribution does xbar - mu have?

and then how does this help for the question?


Ah I think I've finally got it, thanks so much for your help! So the distribution would be mean 0 variance 9/n then I would use z being less than 1-0/ square root of 9/n with the critical value being 2.3263 then solve for n from there? :smile:
Original post by economicss
Ah I think I've finally got it, thanks so much for your help! So the distribution would be mean 0 variance 9/n then I would use z being less than 1-0/ square root of 9/n with the critical value being 2.3263 then solve for n from there? :smile:


:borat: well done
Hi, on question 7b of this paper https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202006%20QP%20-%20S3%20Edexcel.pdf does anyone know why it isn't multiplied by 10 divided by the square root of n since the mark scheme just shows the z value multiplied by sigma, however I thought this was normally divided by root n for confidence limit questions? Thanks :smile:
Original post by economicss
Hi, on question 7b of this paper https://869d950bf149eefd5cd2652b400160ceb38ca5c7.googledrive.com/host/0B1ZiqBksUHNYVGVDMmVJYzVnRnc/June%202006%20QP%20-%20S3%20Edexcel.pdf does anyone know why it isn't multiplied by 10 divided by the square root of n since the mark scheme just shows the z value multiplied by sigma, however I thought this was normally divided by root n for confidence limit questions? Thanks :smile:


It's not the confidence interval of the mean, it's just the confidence interval for the data. :h:

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