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# The Official Edexcel S2 Jan 2010 Thread watch

1. No they asked for the probabiltity x<0 which is px<=-1 so the answer is 1/6

F(0) = P(X<=0) they asked for p(x<0)...so F(0) would not work
2. (Original post by James Greenham)
No they asked for the probabiltity x<0 which is px<=-1 so the answer is 1/6
This method is correct when dealing with discrete distributions ie P(X<0) = P(X<=-1)

However the question is dealing with a continuous distribution where it can be said P(X<0) = P(X<=0)
this is due to the fact that P(X=0) = 0.

hope this helps.
3. (Original post by ben_1991)
This method is correct when dealing with discrete distributions ie P(X<0) = P(X<=-1)

However the question is dealing with a continuous distribution where it can be said P(X<0) = P(X<=0)
this is due to the fact that P(X=0) = 0.

hope this helps.

Ben is correct in this case, if you have been taught S2 from the new Heinemann books, it isn't clearly stated that when P(X<0) = P(X<=0) for continuous distribution and P(X<0) = P(X<=-1) ONLY for discrete distributions.
If you have access to the old Heinemann series (blue book) it is more explicitly stated.

I got critical Region 2 and 17
Did the Mean probabilities wrong for the last question
and Robot question I did conditional but got over 1 so flipped the fraction (for no apparent reason), (well actually so I would get less than one) ...

what marks am i bound to get anyone? x
4. (Original post by ben_1991)
ill add my 2 cents to the questions people seem to be also disagreeing on!

(2a) P(X<0) = 1/3

(3d) same as part (3b) due to independence

(4b) F(x)=
0 for x<0
1/27(x^3-3x^2+6x) for 0<x<=3
1/3(x-1) for 3<x<=4
1 for x>4

(6b+6c) critical regions X<=2 X>=16 sig level 0.85%
i got the independance thing wrong as i said 3d=3c by mistake

whats the definition for critical regoin by the way???
5. (Original post by kosy91)
whats the definition for critical regoin by the way???
i put:
the critical region is the range of value where if the test statistics lies, would lead to the rejection of the null hypothesis, H0.
6. (Original post by ben_1991)
i put:
the critical region is the range of value where if the test statistics lies, would lead to the rejection of the null hypothesis, H0.
i said critical region contains critical values that lead to rejection of null hypothesis(H0)
7. so how did everyone find it? im not too sure
8. (Original post by Moa)
Edexcel S2 - Tuesday 19 January 2010 Paper: (warning, very poor quality)
Spoiler:
Show

noooooooooooooooo...

I got as a Critical region C<=1 and C=>11

pleas tell me that is not c<=2 and C=>16 !!!!!!!!!!!!

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOO
9. has any1 posted the unofficial markscheme of jan 2010 yet?? pls let me know :|
10. i doubt thay have
11. (Original post by James Greenham)
No they asked for the probabiltity x<0 which is px<=-1 so the answer is 1/6

F(0) = P(X<=0) they asked for p(x<0)...so F(0) would not work
no its continuous distribution so you dont change the P(X<0) to P(X<=-1)
12. (Original post by [email protected]@y)
noooooooooooooooo...

I got as a Critical region C<=1 and C=>11

pleas tell me that is not c<=2 and C=>16 !!!!!!!!!!!!

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOO
sory but i found the second one
13. Has anyone got a good copy of the paper and some solutions yet?
14. for question three did people use binomial or poisson??
15. (Original post by viki_91)
for question three did people use binomial or poisson??
poisson
16. (Original post by john1234567)
poisson
garr i knew it everyone used poisson i dont even know why i used binomal because i know its wrong. do u think i will lose all ten marks?
17. (Original post by viki_91)
garr i knew it everyone used poisson i dont even know why i used binomal because i know its wrong. do u think i will lose all ten marks?
i suppose if you used the right principles you might get a few method marks
18. (Original post by viki_91)
garr i knew it everyone used poisson i dont even know why i used binomal because i know its wrong. do u think i will lose all ten marks?
my freind did that too.

but the word 'rate' at the start of the question gave the hint that it was poisson
19. i knew i got the critical region wrong.. lol.. i got the actualy significance as 0.. haha.. yeh probs looked at wrong bit of table! gosh.. lol.. hmmm..
20. i have lost 5 marks. not more hopefully.
how much do you guys think my final UMS will be? can i expect anything over 90? or will it be 86-88-ish??

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