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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Euclidean)
I think it does work using [quote=Euclidean][s]woo[/s][/quote] but thanks!
2. (Original post by SeanFM)
I think it does work using but thanks!
Ooh It does indeed

At least they're more likely to see it with two tags
3. (Original post by SB0073)
No it can be integers too. You only need to square when its the variance and its not a combination. The majority fall into two types of questions ill give you an example, sort of from above. Find the probability that the mens height is 2 times greater than women's height. The thing you would consider is P(M>2W) Therefore becomes P(M-2W>0) Let X=M-2W, Then E(X) = E(M)-2E(W) and Var(X)= Var(M) + 2^2Var(W)

However if the question were to be two women are selected find the probability that the mans height is greater than the total of the two women? you would consider P(M>W1+W2) Which becomes P(M-W1-W2>0) So let Y=M-W1-W2 Then E(Y)= E(M)-E(W1)-E(W2) But because W1 and W2 have the same distribution its E(Y)= E(M) -2E(W) and Var(Y)=Var(M)+Var(W1)+Var(W2) Apply same rule and Var(Y)=Var(M)+2Var(W)

Hopefully thats all correct and some sort of help
Great clarification.

Could I justask you that if they said what is the probablility that a man weighs more than 5/8 of a woman, would we square the 5/8 for the variance or not. Thank you agagin for that post.
4. "Consider the heights of students atTiffin, say with σ^2=0.4m

Ifthe sample size was 1,what (on average) would the variance of our sample be? What does this tell usabout our use of the sample variance to represent the population variance?
Variance of sample is 0. Thereforeit must be a biased estimator, because on average the variance of the sample(i.e. 0) is not equal to the variance of the population."Could someone please explain this I don't fully understand how the variance is 0?
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5. (Original post by L'Evil Wolf)
"Consider the heights of students atTiffin, say with σ^2=0.4m

Ifthe sample size was 1,what (on average) would the variance of our sample be? What does this tell usabout our use of the sample variance to represent the population variance?
Variance of sample is 0. Thereforeit must be a biased estimator, because on average the variance of the sample(i.e. 0) is not equal to the variance of the population."Could someone please explain this I don't fully understand how the variance is 0?
----
Is that the full question?
6. How do you know exactly how many degrees of freedom to use in a chi square test?

I can't see why this one uses 4 d.o.f rather than 5

Tagging some people who may be able to help:
Gregorius Zacken SeanFM gagafacea1
7. Only Ch 4 and 5 left. Im killing it

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8. (Original post by physicsmaths)
Only Ch 4 and 5 left. Im killing it

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Going from scratch today? How long you been at it?
9. (Original post by Euclidean)
Tagging some people who may be able to help:
Gregorius Zacken SeanFM gagafacea1
Remember you have to merge classes whose expected frequency is <5.
10. (Original post by Zacken)
Remember you have to merge classes whose expected frequency is <5.
Thank you!
11. (Original post by Euclidean)
Going from scratch today? How long you been at it?
Well i started Ch1 ages ago but didnt resume till now properly. Did Ch3 a few weeks ago for a few days. Just gna do some review exercises on Ch1-3 then start Ch4 tonight.

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12. (Original post by physicsmaths)
Well i started Ch1 ages ago but didnt resume till now properly. Did Ch3 a few weeks ago for a few days. Just gna do some review exercises on Ch1-3 then start Ch4 tonight.

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That's reassuring to hear, I'm no where near as prepared for this as I was for M3 tbh... Gonna be nervous unless I can fix it up in the next week
13. (Original post by L'Evil Wolf)
Great clarification.

Could I justask you that if they said what is the probablility that a man weighs more than 5/8 of a woman, would we square the 5/8 for the variance or not. Thank you agagin for that post.
If we had a Q like that then yes I think we would consider P(M>0.625W) Which would be P(M-0.625W>0) Then say Let X =M-0.625W E(X) would be E(M)-0.625E(W) And Var(X)=Var(M)+0.625^2Var(W)

Sorry about the decimals and bad notation(^2=Squared :P), Not really sure how to write stuff out properly on here.
14. Is it me or are edexcel contradictory. Page 37 they say a continuity correction can be applied if finding the total of an xi. But then EX 3D Q 5B by looking at the answer a continuity correction isn't applied- why is this?

And I just used the clt for that q and just did p(xbar< 100 divided by 35) is it still okay to use that method when asked to find the probably of a sum of?
15. (Original post by SeanFM)
Is that the full question?
Yes, it has the answer in it. Only that is it because there can be no variance of only one sample
16. https://771a1ec81340d97ae9ed29694f73...XZCVmc/CH2.pdf

Anyone know how to solve Ex A Q5 for part b and c. The answers look wrong.
17. (Original post by Rkai01)
Is it me or are edexcel contradictory. Page 37 they say a continuity correction can be applied if finding the total of an xi. But then EX 3D Q 5B by looking at the answer a continuity correction isn't applied- why is this?

And I just used the clt for that q and just did p(xbar< 100 divided by 35) is it still okay to use that method when asked to find the probably of a sum of?
If you could post pictures that would help otherwise someone with the textbook will be able to help you.
18. general answers in S3 do we keep everything to 4dp?
19. I think i broke stats.
But seriously why does route 1 not work. Where is the mistake?

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20. Better image.

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