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    4c) - I got 0.122, so yep i agree
    4d) - i got 0.0024, yep
    4e) mean = 2, variance = 1.8 - yep
    3) 0.0713.

    same for those as well.

    What did people get for the F(x)

    I got x/3 for 0<x<1

    and 2/45x^4 for the 1<x<4 tho people seemed have a constant added on the end :O

    ∫8/45x^3 = 2/45x^4 doesn't it? :rolleyes:
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    (Original post by BlueAngel)
    For d) I used normal.

    Could someone tell me if I was right or wrong?
    i did the same

    does anyone remember the answers to q 5?
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    (Original post by Neutrinohunter)
    ∫8/45x^3 = 2/45x^4 doesn't it? :rolleyes:
    You had to take into account that F(x) is cumulative and therefore you had to add the maximum value from the previous bit of the distribuiton (i.e. 1/3) and integrate between the lower limit (1) and the max possible value (infinity or x)....at least I think thats correct :confused:
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    you needed a 1/3 constant at the end
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    Oh well i still seemed to get the right answer for the median, can't see how i can lose about 15 marks or whateva on the paper to not get an A but i don't wanna be too confident, cos many people found the paper rele easy
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    (Original post by Leekey)
    That was either the easiest S2 paper I have ever sat or it was the hardest. I think I did everything correctly but I kept waiting for a difficult git of a question and it just didn't seem to happen (think I might have failed due to the fact that I found it too easy).... :confused:
    hey leekey... told ya it wont be a problem... how did you find your resits? u should get your A then
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    (Original post by clare_m)
    indeed, you are correct

    Are you talking to me?
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    (Original post by S1M)
    hey leekey... told ya it wont be a problem... how did you find your resits? u should get your A then

    Wassup S1M, it was 'easy' init..... LOL
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    (Original post by S1M)
    hey leekey... told ya it wont be a problem... how did you find your resits? u should get your A then
    God I hope I get at least a B. I've put EVERYTHING I have into maths this time round and I just pray its going to get me into uni. The resits were all fairly decent (except S1 because of my inability to so any stats), I think my P1 mark will boost my grade and make up for a shocker in P3 or S2 though (hopefully not both)!!!

    How have you gone on today? :confused:
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    (Original post by Leekey)
    God I hope I get at least a B. I've put EVERYTHING I have into maths this time round and I just pray its going to get me into uni. The resits were all fairly decent (except S1 because of my inability to so any stats), I think my P1 mark will boost my grade and make up for a shocker in P3 or S2 though (hopefully not both)!!!

    How have you gone on today? :confused:
    Yeh, i thought it was ok too... other than that 1st question i think ill get most of the marks... so you think your 3 days revision payed off then?

    (Original post by DaKe)
    Wassup S1M, it was 'easy' init..... LOL
    lol... shut up m8...
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    For the questions where you had X~B(100,0.1) and you were supposed to approximate it to find P(X > 15) or something, should it have been approximated as normal or poisson?

    I thought you could do poisson as "n is large and p is small"
    or you could do normal as np > 5 and n(1-p) > 5

    so which should've been used? or would either have been ok?
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    (Original post by S1M)
    so you think your 3 days revision payed off then?
    Based on the fact that 3 days ago I couldn't do probability density functions and my hypothesis testing was shakey and now I'm feeling pretty decent about the exam, I think that it worked pretty well yeah!!!
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    I'm wondering if that was too easy to be true! Especially the first 6 qus. I tried to remember my answers, wrote some down and I think I got:
    1) [definitions]
    2) a: 0.54, b:1.5, c:2.083
    3) don't remember
    4) a:Binomial rules, b:X~B(70, 0.1), c:0.1216, d:0.0024, e(x)=2 & Var(x)=0.8, f:0.0487 (or something like that)
    5) a:critical value def, b:0.9907, c:0.947, d:0.0733
    6) a: X~Po(0.05), b:0.251, c:0.0045, d:0.1562
    7) a:1.269, b:x/3 & something involving 45, c:1.831, d: negitive skew.

    If any don't look right, then I may have either totally effed it up or remembered them wrong!
    Did anyone get the same?
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    (Original post by davedave)
    For the questions where you had X~B(100,0.1) and you were supposed to approximate it to find P(X > 15) or something, should it have been approximated as normal or poisson?

    I thought you could do poisson as "n is large and p is small"
    or you could do normal as np > 5 and n(1-p) > 5

    so which should've been used? or would either have been ok?
    i used poisson for that... i was unsure which one... because both seemed feasible imo... but as i noticed n was large... so i went for poisson... not sure if "p is small" enough though... thats why i had my doubts... coz that means the mean is 10 and the variance is 9... for poisson mean is equal to variance... so as thats quite a big % difference between 9 and 10... i thought it could be normal too... but i ended up doing poisson anyway... well i tryed the normal quickly on my calculator and it gave a slightly lower answer anyway... so if poisson is wrong hopefully we should still get some marks...
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    (Original post by davedave)
    For the questions where you had X~B(100,0.1) and you were supposed to approximate it to find P(X > 15) or something, should it have been approximated as normal or poisson?

    I thought you could do poisson as "n is large and p is small"
    or you could do normal as np > 5 and n(1-p) > 5

    so which should've been used? or would either have been ok?
    I used Poisson cause I prefer it, but I double checked with the Normal & only got 0.0001 difference, so I don't think it matters. It works for both.
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    MATHS IS OVER!! HOORAH!!

    So anyway, big stress now. I'm trying to get last year's mark boundary thingys off the edexcel site, but i dont think i have adobe acrobat (?) on my computer - that or it wont work.

    can anyone have a look and post them up for p2-3 and s1-2?

    i really dont think ive got my a overall....

    this paper was fine though - ive just realised i got the skew bit wrong - i thought mode<mean<median but its mode<median<mean so thats 2 marks gone. im not hunting for any more missed marks - ill get upset
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    When approximating from a Binomial to a Normal it is best if the probability is about 0.5 to ensure symmetry (I think anyway)!!! Since 0.1 wasn't anywhere near 0.5, I decided to use a poisson.
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    how did u work out the median?

    this is wot i did:

    f(x) = 1/3 0<=x<1
    = 8x^(3)/45 1<=x<=2
    = 0 elsewhere

    the median will be in the second bit

    so integrate with limits m and 1 making it equal to a half

    rearrange to make x subject

    and you should get a quartic root

    someone validate me
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    (Original post by Louise87)
    I used Poisson cause I prefer it, but I double checked with the Normal & only got 0.0001 difference, so I don't think it matters. It works for both.

    np>10 so use normal approximation

    in the exam u usually use poisson if p is less than 0.1

    0.1 is fairly central
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    (Original post by mabs)
    how did u work out the median?

    this is wot i did:

    f(x) = 1/3 0<=x<1
    = 8x^(3)/45 1<=x<=2
    = 0 elsewhere

    the median will be in the second bit

    so integrate with limits m and 1 making it equal to a half

    rearrange to make x subject

    and you should get a quartic root

    someone validate me
    I remember something like X^4 = 4.74 of something like that....
 
 
 
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