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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Ayman!)
I think I sorta figured it out. Quota is completely random in who it interviews (no random numbering or such) while stratified is systematic. Thank you.
The textbook says that it's a non-random process though?
2. (Original post by Ayman!)
I think I sorta figured it out. Quota is completely random in who it interviews (no random numbering or such) while stratified is systematic. Thank you.
The notes say that quota is non-random (it must be due to how it is done) whereas though things are numbered when you're stratifying, the numbers that are picked should be random. So I'm not too sure what Edexcel are trying to say.
3. (Original post by Zacken)
The textbook says that it's a non-random process though?
(Original post by SeanFM)
The notes say that quota is non-random (it must be due to how it is done) whereas though things are numbered when you're stratifying, the numbers that are picked should be random. So I'm not too sure what Edexcel are trying to say.
Surely picking random members of the population to interview is a random process? Looks like I don't quite get it yet.
4. (Original post by Ayman!)
Surely picking random members of the population to interview is a random process? Looks like I don't quite get it yet.
I think it comes from the 'people who don't respond aren't recorded' and that you might interview 11 people for a quota of 10 because the 8th person didn't respond

Sounds like rubbish anyway.
5. (Original post by SeanFM)
Sounds like rubbish anyway.
This is the only bit of S3 that makes me go Reminds me of A-level Biology. Wish I could have done S4 instead.
6. (Original post by Ayman!)
This is the only bit of S3 that makes me go Reminds me of A-level Biology. Wish I could have done S4 instead.
The good thing is, if it comes up you can make something up, similar to stratified sampling but with an interviewer, and it'll probably be right (and just remember interview bias / non responses not recorded).
7. (Original post by SeanFM)
Yes, but they're concerned with ranks. Notice that the higher the (number of) rank, the greater the number of pages.
I always thought of it in my head as a graph so the claim would show a negative correlation(as one decreases the other increases). Not too sure I get it though.
8. (Original post by Rkai01)
I always thought of it in my head as a graph so the claim would show a negative correlation(as one decreases the other increases). Not too sure I get it though.
I see what you're saying, it's a bit confusing to me as well.

I guess you have to think of a graph with (1,50), (2,212)...(10,317), but double check with another example from a past paper or textbook.
9. Is EX2A Q5 just wrong with the random numbers questions for part b and c.
10. also which papers do people consider the hardest - would like to use them as mock papers.

And are the solomon press papers worth doing

11. Pls explain this Lol

Solved: Thanks Zacken
12. (Original post by L'Evil Wolf)

Pls explain this Lol

Solved: Thanks Zacken
I think solutions bank is wrong and you're right, as don't you only square the constants if you're scaling the distribution? Not completely sure
13. (Original post by economicss)
I think solutions bank is wrong and you're right, as don't you only square the constants if you're scaling the distribution? Not completely sure
Actaully S.B. was right lol

You use from S1: Var(aX + bY) = a^2Var(X) + b^2Var(Y).

The operation is thus:

Var(2X1+3X10/5) = Var(0.4X1 + 0.6X10) = (0.4)^2 Var(X1) + (0.6)^2 Var(X10)

=13/25 (sigma^2)

-Thanks to Zacken and ayman for helping correct me
14. (Original post by L'Evil Wolf)
Actaully S.B. was right lol

You use from S1: Var(aX + bY) = a^2Var(X) + b^2Var(Y).

The operation is thus:

Var(2X1+3X10/5) = Var(0.4X1 + 0.6X10) = (0.4)^2 Var(X1) + (0.6)^2 Var(X10)

=13/25 (sigma^2)

-Thanks to Zacken and ayman for helping correct me
Ah I see, thank you
15. If the mean is written as sigma x /n then we do not regard it as a statistic - only mu would not be a statistic
16. (Original post by L'Evil Wolf)
If the mean is written as sigma x /n then we do not regard it as a statistic - only mu would not be a statistic

What is the definition of a statistic?
17. (Original post by SeanFM)

What is the definition of a statistic?
I think so lol, that didn't make much sense though Lol
18. (Original post by L'Evil Wolf)
I think so lol, that didn't make much sense though Lol
Could you rephrase it?

What is the definition of a statistic?
19. (Original post by L'Evil Wolf)
Actaully S.B. was right lol

You use from S1: Var(aX + bY) = a^2Var(X) + b^2Var(Y).

The operation is thus:

Var(2X1+3X10/5) = Var(0.4X1 + 0.6X10) = (0.4)^2 Var(X1) + (0.6)^2 Var(X10)

=13/25 (sigma^2)

-Thanks to Zacken and ayman for helping correct me
I had just done this ;-;
20. (Original post by SeanFM)
Could you rephrase it?

What is the definition of a statistic?
Statistic = If X1,X2,X3,...,Xn is a random sample of size n from some population, then a statistic T is a random variable consisting of any function of the Xi that involves no other unknown quantities. A stastic must not contain any unknown population paramaters.

Is that okay? Or words to that effect

(Original post by Imperion)
I had just done this ;-;
Lol

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