Edexcel S3 - Wednesday 25th May AM 2016

I think it does work using [noparse] but thanks!

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

"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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Only Ch 4 and 5 left. Im killing it


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Tagging some people who may be able to help:
@Gregorius @Zacken @SeanFM @gagafacea1

Remember you have to merge classes whose expected frequency is <5.

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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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.

Is that the full question?

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?