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Stats 2 (S2) OCR (not MEI) 22nd June 2012

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    (Original post by studentofskhs)
    Yes . Btw how did you do 8iii)? I done 1-(p(x=0)+p(x=1)+p(x=2)) using s1 binominal rules. Not sure if i'm right though. I got a small value like 0.01 ish
    I think i did that it was a binomial of (20, 0.05) and then i did greater than or equal to 4 which is 1 - less than or equal to 3. Don't know if that's right though.
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    Here are my answers:

    1) Random number generator 000 to 999

    2 Var(V)=173

    3) P(X>=7) = 0.0664 larger than 0.025 ACCEPT H0

    4) i) independent
    ii) 0.114
    iii) 0.422
    iv) 0.268

    5) 1.1153 < 1.645 ACCEPT H0

    6) i) 0.0449
    ii) 0.0494

    7) ii) a=6 (k=1/72)

    iii) Var(X) = 1.35

    8) i) CR >33.1
    ii) Type I error
    iii) 0.0159 , mean not 30 because probability so small
    iv) mean is 33.58

    Any thoughts guys?
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    (Original post by jamib0y)
    Here are my answers:

    1) Random number generator 000 to 999

    2 Var(Vbar)=173 I think you mean Var(V), not V bar.

    3) P(X>=7) = 0.0664 larger than 0.025 ACCEPT H0

    4) i) independent
    ii) 0.114
    iii) 0.422
    iv) 0.268

    5) 1.1153 < 1.645 ACCEPT H0

    6) i) 0.0449
    ii) 0.0494

    7) ii) a=6 (k=1/72)

    iii) Var(X) = 1.35

    8) i) CR >33.1
    ii) Type I error
    iii) 0.0159
    iv) mean is 33.58

    Any thoughts guys?
    I've forgotten many answers - those that I remember, I agree with.
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    (Original post by CraigKirk)
    I've forgotten many answers - those that I remember, I agree with.
    Yeah, that's what I mean
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    (Original post by jamib0y)
    Here are my answers:

    1) Random number generator 000 to 999

    2 Var(Vbar)=173

    3) P(X>=7) = 0.0664 larger than 0.025 ACCEPT H0

    4) i) independent
    ii) 0.114
    iii) 0.422
    iv) 0.268

    5) 1.1153 < 1.645 ACCEPT H0

    6) i) 0.0449
    ii) 0.0494

    7) ii) a=6 (k=1/72)

    iii) Var(X) = 1.35

    8) i) CR >33.1
    ii) Type I error
    iii) 0.0159
    iv) mean is 33.58

    Any thoughts guys?
    From vaguely remembering my answers, i think it all looks good.
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    for 8)iii),
    Does anyone know for sure whether you're supposed to put that the mean is 30 or not 30?
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    (Original post by Bwob)
    for 8)iii),
    Does anyone know for sure whether you're supposed to put that the mean is 30 or not 30?
    Yeah, I put down it's not 30 because the probability is so small
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    What did people say for 7 i)?
    I don't think I expressed myself very well. It's generally the questions with words involved I didn't like - again 8iii) I got 0.0155 or something, but I said since the probability is small, it probably is 30, which goes against what most people have been saying :/
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    (Original post by Bb King)
    What did people say for 7 i)?
    I don't think I expressed myself very well. It's generally the questions with words involved I didn't like - again 8iii) I got 0.0155 or something, but I said since the probability is small, it probably is 30, which goes against what most people have been saying :/
    Graph of x^2, starting from 0 and ending at a.
    I commented that as X takes ranges closer to a, the probability of X increases. If ranges of X fall below 0 or above a, the probability of X is zero.
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    (Original post by JongKey)
    From vaguely remembering my answers, i think it all looks good.
    im so sillyy!! i tried to find the critcial region for question 3 and found x-1 =7 and being me said therfore x=7 and rejected h0 :/ . 3 markss gonee. sigh.
    think i got 68 or 67 from the looks of thingss.. but ive probs made some very silly mistakes :/
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    Can you lose marks for giving a greater degree of accuracy than 3 significant figures?
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    (Original post by Matthew692692)
    Can you lose marks for giving a greater degree of accuracy than 3 significant figures?
    In general, no, as long as your answer rounds to the answer given in the mark scheme, or falls in a range given in the mark scheme.
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    (Original post by CraigKirk)
    In general, no, as long as your answer rounds to the answer given in the mark scheme, or falls in a range given in the mark scheme.
    Thank god for that, I usually give them to more :P
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    (Original post by Matthew692692)
    Thank god for that, I usually give them to more :P
    Yeah, I gave many of mine today to 4sfs, as in statistics mark schemes there often tend to be four decimal places in the answer.
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    (Original post by jamib0y)
    Here are my answers:

    1) Random number generator 000 to 999

    2 Var(Vbar)=173

    3) P(X>=7) = 0.0664 larger than 0.025 ACCEPT H0

    4) i) independent
    ii) 0.114
    iii) 0.422
    iv) 0.268

    5) 1.1153 < 1.645 ACCEPT H0

    6) i) 0.0449
    ii) 0.0494

    7) ii) a=6 (k=1/72)

    iii) Var(X) = 1.35

    8) i) CR >33.1
    ii) Type I error
    iii) 0.0159 , mean not 30 because probability so small
    iv) mean is 33.58

    Any thoughts guys?
    Everything correct, well done. :clap2:

    Bits you've missed out:

    1. Need to mention 15 unique numbers.

    2. (i) should be Var(V), but you wouldn't lose a mark
    (ii) "We don't know the distribution of V"; "n>30 so CLT applies"

    6. (i) Normal approximation is suitable as np and nq both exceed 5.

    7. (i) positive quadratic graph between x=0 and x=a going through (0,0) and not extending below x=0 or above x=a. Then something along the lines of "X can take any value between 0 & a (but not including 0). X is more likely to take values closer to a than to 0."
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    (Original post by Mr M (jr))
    Everything correct, well done. :clap2:

    Bits you've missed out:

    1. Need to mention 15 unique numbers.

    2. (i) should be Var(V), but you wouldn't lose a mark
    (ii) "We don't know the distribution of V"; "n>30 so CLT applies"

    6. (i) Normal approximation is suitable as np and nq both exceed 5.

    7. (i) positive quadratic graph between x=0 and x=a going through (0,0) and not extending below x=0 or above x=a. Then something along the lines of "X can take any value between 0 & a (but not including 0). X is more likely to take values closer to a than to 0."
    Surely question 3 - it was a 1 tail test as it said 'Test at the 5% sig level that the study is correct'.

    I know it doesn't affect the overall result (I checked this) but you lose 2 marks for doing it as a 2 tail rather than 1 tail?
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    (Original post by Mr M (jr))
    Everything correct, well done. :clap2:

    Bits you've missed out:

    1. Need to mention 15 unique numbers.

    2. (i) should be Var(V), but you wouldn't lose a mark
    (ii) "We don't know the distribution of V"; "n>30 so CLT applies"

    6. (i) Normal approximation is suitable as np and nq both exceed 5.

    7. (i) positive quadratic graph between x=0 and x=a going through (0,0) and not extending below x=0 or above x=a. Then something along the lines of "X can take any value between 0 & a (but not including 0). X is more likely to take values closer to a than to 0."
    Yeah, thanks, I just didn't have the time to write all the above but got it all! Thanks!
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    (Original post by CraigKirk)
    Yeah, I gave many of mine today to 4sfs, as in statistics mark schemes there often tend to be four decimal places in the answer.
    Annoyingly for some reason I gave the final one to 3sfs though :/ I NEVER do that in stats!!
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    FFS, couldn't have gotten an easier paper and I still managed to muck it up; lost a good 10 marks at the least. Well, at least it'll contribute towards bringing the grade boundaries down (by whatever negligible value) for all of you concerned.
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    (Original post by Matthew692692)
    Annoyingly for some reason I gave the final one to 3sfs though :/ I NEVER do that in stats!!
    I nearly did that too, managed to see that right at the end when I was checking :P

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