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Tips for S2 exam!!!!!!

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Reply 20
Avatar for Adil Bhai
Adil Bhai
OP
ur right emma but don't the distribution questions always have to be to 4dps?
Reply 21
Avatar for Bhaal85
Bhaal85
9
Before you enter the exam, you should:

Have a break, have a kit kat.
Reply 22
Avatar for Bhaal85
Bhaal85
9
Adil Bhai
ur right emma but don't the distribution questions always have to be to 4dps?


For your working out you would most definitely use more than 3 significant figures, however for your final answer you only have to give it to 3 sf, unless otherwise stated.

CLT = Central Limit Theorem, if the original distribution follows a normal then you can use the CLT regardless the size of n.
Reply 23
Avatar for zxcvbnm
zxcvbnm
i always gine answers to 4 dp because all the probaliities in tables are given to 4dp
When sketching a pdf/cdf, make the lines along the x-axis nice and thick, or marks will be lost. AND DON'T BE STUPID LIKE ME, LABEL THE AXES.

like if it says f(x) = 0 for x < 1 then there has to be a thick line going from 1 to negative x along the x-axis (my teacher, who used to mark a-level papers, told me this).

If you're doing a question where X~B(n,p) or X~N or or X~Blah de blah
always write what x actually is.

Learn the definitions of things like sampling distribution, statistic, population, samlping unit, etc, learn the conditions for binomial and poisson - there's always some kind of wordy question.

Good luck everyone!
Reply 25
Avatar for Bhaal85
Bhaal85
9
Continunuity corrections are a biggy too.
Another thing I just remembered, which I wouldn't have known if I hadn't seen it on a past paper markscheme:

The value of p that will give the most accurate estimate when approximating the binomial distribution by a normal distribution is p = 0.5, as this will give a symmetrical binomial distribution.

Usually, I think the "Approximation Hierarchy" goes something like:

Binomial can be approximated by Poisson for small values of p and large values of n, and this is generally the method to use. If this is not practical for the question (i.e., required values not in the table), then Normal can be used (providing np>5 and np(1-p)>5.

Poisson can be approximated by Normal for lambda > 10.

Disclaimer: I'm quite sure this is right, but if it's not, may I never eat ice-cream again.

Dagnabbit, another thing - when approximating using Normal, don't forget to change the values accordingly, like

X~B(n, p)
P(X<12)
becomes
P(Z<11.5) where Z~N(np, np(1-p))
Reply 27
Avatar for ZoGgEr!
ZoGgEr!
and don't forget to minus the square of the mean, I always do that on variance of a pdf...

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