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Edexcel S3 - Wednesday 25th May AM 2016

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Original post by Ayman!
Apologies for the slow replies, my 'tex is not that good. :tongue: But yes - that is precisely what I meant. You can't jump straight into that because the mean is dependent on the individual Xis, but each Xi isn't dependent on each other - they're all independent units. That's why we can go Var(4U1−U2−⋯−U55)=125[Var(4U1)+Var(U2)+⋯+Var(U5)]\mathrm{Var\left ( \frac{4U_{1}-U_{2}-\cdots -U_{5}}{5} \right )} = \frac{1}{25} \left[ \mathrm{ Var\left (4U_{1} \right )+Var\left ( U_{2} \right )+\cdots +Var\left ( U_{5} \right ) } \right]. That's my interpretation of what's going on here, at least. I'm also curious as to what @13 1 20 8 42 says.


Original post by 1 8 13 20 42
Yeah it's basically that the individual Ui are independent so the point of expressing the mean in terms of them is that you can then use the standard expectation algebra


Thank you both, I can't give you anymore rep @13 1 20 8 42


PRSOM
I really hope we get systematic and random number sampling questions instead of the other quota/lottery/whatever crap.

Also, I managed to find IAL June 15 harder than normal June 15. What even. I reckon it's the length of the papers, I preferred the 6 question UK paper over the 8 question IAL paper. Hope we get something like the former for the real thing.
Original post by Zacken
I really hope we get systematic and random number sampling questions instead of the other quota/lottery/whatever crap.

Also, I managed to find IAL June 15 harder than normal June 15. What even. I reckon it's the length of the papers, I preferred the 6 question UK paper over the 8 question IAL paper. Hope we get something like the former for the real thing.


What made IAL 15 harder, just the length? I got fed up of the UK paper despite it being 6 questions as the last one was quite longwinded, I think 7 is ideal
Original post by 1 8 13 20 42
Yeah it's basically that the individual Ui are independent so the point of expressing the mean in terms of them is that you can then use the standard expectation algebra


Thank you. :biggrin:

Original post by Zacken
I really hope we get systematic and random number sampling questions instead of the other quota/lottery/whatever crap.


Also, I managed to find IAL June 15 harder than normal June 15. What even. I reckon it's the length of the papers, I preferred the 6 question UK paper over the 8 question IAL paper. Hope we get something like the former for the real thing.


There was nothing too difficult in the IAL, though. It was lengthy I think but high boundaries.
Original post by Euclidean
What made IAL 15 harder, just the length? I got fed up of the UK paper despite it being 6 questions as the last one was quite longwinded, I think 7 is ideal


Original post by Ayman!
There was nothing too difficult in the IAL, though. It was lengthy I think but high boundaries.


Yeah, nothing difficult, just the combination of boredom and doing it at 3 a.m that made dropped me ~4 marks from silly mistakes whereas the 6 questions in UK 15 were fun and enjoyable (towards the end, at least).
Original post by Zacken
Yeah, nothing difficult, just the combination of boredom and doing it at 3 a.m that made dropped me ~4 marks from silly mistakes whereas the 6 questions in UK 15 were fun and enjoyable (towards the end, at least).


Enjoyable and stats don't go in the same paragraph mate. Just stop it please.



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How come all of Arseys stuff is take down?


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I haven't managed to find the June 15 IAL paper anywhere. Where are you guys finding it?
Original post by Nijuuninichi
I haven't managed to find the June 15 IAL paper anywhere. Where are you guys finding it?


Edexcel website.
Original post by Zacken
Edexcel website.


Oh, I didn't think it would be on there. Thank you! :biggrin:
when testing if a normal distribution is a good model, the classes some some times have a gap in between of 1, for example, classes would be: >1, 2-4, 5-7,..., and the book says to do the continuity correction so the classes are now: >1.5, 1.5-4.5, 4.5-7.5,... When the classes dont have the gap between and they are for example: <3, 3-5, 5-6,.. do we just not have to do anything to the classes and work out the Ei from these?
Original post by connorbarr
when testing if a normal distribution is a good model, the classes some some times have a gap in between of 1, for example, classes would be: >1, 2-4, 5-7,..., and the book says to do the continuity correction so the classes are now: >1.5, 1.5-4.5, 4.5-7.5,... When the classes dont have the gap between and they are for example: <3, 3-5, 5-6,.. do we just not have to do anything to the classes and work out the Ei from these?


With continuous probability distributions like the Normal:

P(a≤X≤b)=P(a<X<b)P( a \leq X \leq b) = P( a < X < b)

So you can work out the expected values without needing to do anything
Original post by Euclidean
With continuous probability distributions like the Normal:

P(a≤X≤b)=P(a<X<b)P( a \leq X \leq b) = P( a < X < b)

So you can work out the expected values without needing to do anything


ye i get that but look at 4c in this http://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Exam%20materials/6691_01_que_20130613.pdf there are no gaps between the classes but in the textbook there are examples of gaps so the textbook has done the continuity correction, for questions like this where there is no gap do we just leave it as it is and work out Ei from here?
Original post by connorbarr
ye i get that but look at 4c in this http://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Exam%20materials/6691_01_que_20130613.pdf there are no gaps between the classes but in the textbook there are examples of gaps so the textbook has done the continuity correction, for questions like this where there is no gap do we just leave it as it is and work out Ei from here?


Original post by Euclidean
So you can work out the expected values without needing to do anything


See above
Original post by physicsmaths
Enjoyable and stats don't go in the same paragraph mate. Just stop it please.



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Disagree :tongue: what other exam do you get such lovely prose? :tongue: except maybe those series questions in C1/C2.
Original post by Euclidean
See above


ok message received, but when there are gaps in the classes you do have to do a continuity correction yes?
Original post by Ayman!
Apologies for the slow replies, my 'tex is not that good. :tongue: But yes - that is precisely what I meant. You can't jump straight into that because the mean is dependent on the individual Xis, but each Xi isn't dependent on each other - they're all independent units. That's why we can go Var(4U1−U2−⋯−U55)=125[Var(4U1)+Var(U2)+⋯+Var(U5)]\mathrm{Var\left ( \frac{4U_{1}-U_{2}-\cdots -U_{5}}{5} \right )} = \frac{1}{25} \left[ \mathrm{ Var\left (4U_{1} \right )+Var\left ( U_{2} \right )+\cdots +Var\left ( U_{5} \right ) } \right]. That's my interpretation of what's going on here, at least. I'm also curious as to what @13 1 20 8 42 says.


Im also confused by this. I thought because U1 U2... were all independant of each other then you don't square the constant of variation? Why is it not just over 5?
Original post by connorbarr
ok message received, but when there are gaps in the classes you do have to do a continuity correction yes?


Yeah :smile:

Only if you're using a continuous distribution though!
Original post by Euclidean
See above


i keep on applying the 0.5 **** since thats what the book did in examples.
Original post by Euclidean
Yeah :smile:

Only if you're using a continuous distribution though!


sound thanks, so i should do it for continuous uniform as well if there are gaps?

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