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# The Official Edexcel S2 Revision Thread! (22/06/05 PM) watch

1. GUYS! Important question. I keep doing past papers, and use the statistical tables at the back of my S2 book for the Binomial...

HOWEVER, I keep having to not do questions because n = 25 or something greater than 20, and so the table at the back is not sufficient. I take it therefore, that in the formulae booklet, we are given the tables for n = 25??? Please check someone!
2. yes we are
3. (Original post by RobbieC)
GUYS! Important question. I keep doing past papers, and use the statistical tables at the back of my S2 book for the Binomial...

HOWEVER, I keep having to not do questions because n = 25 or something greater than 20, and so the table at the back is not sufficient. I take it therefore, that in the formulae booklet, we are given the tables for n = 25??? Please check someone!
yes.
the formulae booklet has tables for a range of values between 5 n 50
4. Thank GOD! Lol I wondered why I couldnt do those questions, AT ALL!!!

I need to learn some definitions... I cant define a statistic properly... but it sounds right to me
5. (Original post by KAISER_MOLE)
I've just had a thought, with multi pdf thingies, do they ask, and furthermore, what does one do if they ask for the mean and the variance? Is it just top of top range minus bottom of bottom range with definite integrals?
if its the mean, then u add the integrals with their respective limits
(get the mean for each bit as u wud for just one pdf n add)

for variance its the same thing except that u multiply through by x² rather than x to get E(x²)

then the usual Var(x) = E(x²) - {E(x)}²
6. (Original post by hajira)
if its the mean, then u add the integrals with their respective limits
(get the mean for each bit as u wud for just one pdf n add)

for variance its the same thing except that u multiply through by x² rather than x to get E(x²)

then the usual Var(x) = E(x²) - {E(x)}²
is it definitely add, not find the average of?

because in this case say the mean might be; for the first is 3.5 and the mean for the second is 7.5, you end up with 11, outside the range.
8. (Original post by tobyclark)
is it definately add, not find the average of?
think about it in terms of the graph..u'r getting the avg for one section n then the next section...for the whole big section, its wud b add the two
dunno how convincing that sounds, but yeah u DO add
but be careful about using the right ranges

good luck
9. sorry guy if im being annoying, but....
for var(x) is it
1. Var(x) of a + Var(X) of b
or
2.
e(X^2) of a - e(x)^2 of a
+
e(X^2) of b - e(x)^2 of b
10. groovy, cheers Hajira, never come across it before, but, just incase
11. from f(x)--------->F(x) do i intergrate??
12. (Original post by amimeera)
from f(x)--------->F(x) do i intergrate??
yes, x as the top limit and the lower limit of the pdf as the lower limit
13. Good luck for tomorrow, everybody! I spent AGES working out how to do the last part of Review Ex 1 Qu. 22. FINALLY! Wordy questions suck..
14. (Original post by tobyclark)
sorry guy if im being annoying, but....
for var(x) is it
1. Var(x) of a + Var(X) of b
or
2.
e(X^2) of a - e(x)^2 of a
+
e(X^2) of b - e(x)^2 of b
you sound as if you don't understand what a and b are.. they are the upper and lower boundaries of a uniform distribution and so are present in the same distribution.
The variance of a continuous uniform distribution is found by (b-a)²/12 where b is the upper boundary and a is the lower boundary
The variance in a PDF is E(X²) - E(X)², as far as i know there are no a's or b's involved in PDFs
15. (Original post by Featherflare)
you sound as if you don't understand what a and b are.. they are the upper and lower boundaries of a uniform distribution and so are present in the same distribution.
The variance of a continuous uniform distribution is found by (b-a)²/12 where b is the upper boundary and a is the lower boundary
The variance in a PDF is E(X²) - E(X)², as far as i know there are no a's or b's involved in PDFs
sorry, when i said a and b i was referring to the two parts of the p.d.f., sorry very misleading of me to use a and b
16. (Original post by tobyclark)
sorry, when i said a and b i was referring to the two parts of the p.d.f., sorry very misleading of me to use a and b
Oh right, in that case, it's just E(X²) - E(X)², remember that these two values will have already taken into account both the functions (eg to find E(X) you added E(X)a and E(X)b )
17. ok ppl in hypothesis testing when do u reject H0??
18. (Original post by Featherflare)
Oh right, in that case, it's just E(X²) - E(X)², remember that these two values will have already taken into account both the functions (eg to find E(X) you added E(X)a and E(X)b )
perfect, THANK YOU
19. (Original post by amimeera)
ok ppl in hypothesis testing when do u reject H0??
In a one-tailed test, when the probability you work out is less than the significance level you are testing.
In a two tailed test, when x is outside the critical regions you work out
20. ^but u take the probablity closet to the significance level?

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