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

1. (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.

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?
3. (Original post by jamib0y)

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.
4. (Original post by CraigKirk)
I've forgotten many answers - those that I remember, I agree with.
Yeah, that's what I mean
5. (Original post by jamib0y)

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.
6. for 8)iii),
Does anyone know for sure whether you're supposed to put that the mean is 30 or not 30?
7. (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
8. 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 :/
9. (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 , 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.
10. (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 :/
11. Can you lose marks for giving a greater degree of accuracy than 3 significant figures?
12. (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.
13. (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
14. (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.
15. (Original post by jamib0y)

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.

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."
16. (Original post by Mr M (jr))
Everything correct, well done.

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?
17. (Original post by Mr M (jr))
Everything correct, well done.

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!
18. (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!!
19. 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.
20. (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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