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# Edexcel S2 Exam Paper January 2011 14/01/11 Watch

1. (Original post by 20100)
Question 2 seems to be causing a lot of hassle especially for the conclusion part.

I put:

H0: p=0.2
H1: p>0.2

and you reject H0 if P(X>(or equal to)4) <(or equal to) 0.05

which gives you 1 - P(X<(or equal to)3) <(or equal to) 0.05

end result was something like 0.12... <(or equal to) 0.05 which is not true, so there is insufficient evidence to reject H0, meaning we cannot conclude whether the teacher's claim was right or wrong.

Did anyone else put that?
Nope, we have to come to conclusion from rejecting/accepting H0.
2. (Original post by sete)
Your testing to see if the teachers claim is right or wrong, if you accept H0 then what he claims is right, if you reject H0 and accept H1 you are rejecting what he said.
Ah I see... but does that mean I lost a mark for not giving a correct conclusion in contexts?
3. (Original post by snowflakesblues)
I know So was it just 1 mark u lost? Who knows it might still be 100UMS
I don't know how many I lost so yeah. Sorry to hear about the other two marks you lost. should still easily be 90+ with only 3 marks lost. Probably around 95 mark so well done!
4. Hey, everyone. To help stop all the speculation, look in your text books.

In my text book on page 97 (under 4.6 One and Two-tailed tests), there is an example that is practically exactly the same as the question. The only difference was they did it for 5 times or more, instead of our 4. But the question is still the same.
5. (Original post by 20100)
Ah I see... but does that mean I lost a mark for not giving a correct conclusion in contexts?
Depends how they issue the mark.

I.e. Do you gain the mark for just accepting H0?
or For interpreting what accepting H0 meant for the context of the question?

What you said was effectively right, but it depends how they expect us to answer.
6. (Original post by LUCYPOOCEY)
.... just would like some explanation
Most of people here seems to be confused with the wording of that question 2.
I am confident that this is true:
It was 10 questions, so n=10 and 5 answers to each question, p=0.2. Therefore, X--B(10,0.2)
The student achieved 4 correct answers and this is 40% of the paper, but in theory it should be 20% (100*0.2). So he infact got MORE than normal. So the teacher said he was guessing, so we are testing whether or not p >0.2 because the student got 40% which is > than 20%.
.....X--B(10,0.2).....
H1: p = 0.2
Ho: p = >0.2
5% Significance level
Because we are testing its > than 20%, it is:
P(X>=4) = 1 - P(X<=3)....which came to around 0.12....this is >0.05(5%), so Reject H1, not significant and therefore there is sufficient evidence that the probability of of correctly answering is still 0.2. So the teacher's claim is CORRECT in saying that he was guessing.

I hope this can clear the confusion
7. where is the mark shceme for this paper?
8. (Original post by jit987)
Most of people here seems to be confused with the wording of that question 2.
I am confident that this is true:
It was 10 questions, so n=10 and 5 answers to each question, p=0.2. Therefore, X--B(10,0.2)
The student achieved 4 correct answers and this is 40% of the paper, but in theory it should be 20% (100*0.2). So he infact got MORE than normal. So the teacher said he was guessing, so we are testing whether or not p >0.2 because the student got 40% which is > than 20%.
.....X--B(10,0.2).....
H1: p = 0.2
Ho: p = >0.2
5% Significance level
Because we are testing its > than 20%, it is:
P(X>=4) = 1 - P(X<=3)....which came to around 0.12....this is >0.05(5%), so Reject H1, not significant and therefore there is sufficient evidence that the probability of of correctly answering is still 0.2. So the teacher's claim is CORRECT in saying that he was guessing.

I hope this can clear the confusion
The same that I did I defined what X and p represented before doing the hypothesis test to make sure I didn't get confused as I was working through the paper. It was a pretty awesome paper overall though!
9. When is someone going to put up an unofficial markscheme for S2?
10. (Original post by jit987)
Most of people here seems to be confused with the wording of that question 2.
I am confident that this is true:
It was 10 questions, so n=10 and 5 answers to each question, p=0.2. Therefore, X--B(10,0.2)
The student achieved 4 correct answers and this is 40% of the paper, but in theory it should be 20% (100*0.2). So he infact got MORE than normal. So the teacher said he was guessing, so we are testing whether or not p >0.2 because the student got 40% which is > than 20%.
.....X--B(10,0.2).....
H1: p = 0.2
Ho: p = >0.2
5% Significance level
Because we are testing its > than 20%, it is:
P(X>=4) = 1 - P(X<=3)....which came to around 0.12....this is >0.05(5%), so Reject H1, not significant and therefore there is sufficient evidence that the probability of of correctly answering is still 0.2. So the teacher's claim is CORRECT in saying that he was guessing.

I hope this can clear the confusion
Agree with this
11. If anyone can get the paper, I'll do an unofficial mark scheme...
12. (Original post by jit987)
Most of people here seems to be confused with the wording of that question 2.
I am confident that this is true:
It was 10 questions, so n=10 and 5 answers to each question, p=0.2. Therefore, X--B(10,0.2)
The student achieved 4 correct answers and this is 40% of the paper, but in theory it should be 20% (100*0.2). So he infact got MORE than normal. So the teacher said he was guessing, so we are testing whether or not p >0.2 because the student got 40% which is > than 20%.
.....X--B(10,0.2).....
H1: p = 0.2
Ho: p = >0.2
5% Significance level
Because we are testing its > than 20%, it is:
P(X>=4) = 1 - P(X<=3)....which came to around 0.12....this is >0.05(5%), so Reject H1, not significant and therefore there is sufficient evidence that the probability of of correctly answering is still 0.2. So the teacher's claim is CORRECT in saying that he was guessing.

I hope this can clear the confusion
Ohh i get it now, i did the same but with H0 as P = 0.2 and H1 as p = >0.2, but i see why you'd do it the other way around now... Hopefully i'll get some marks for working though. Thanks, well explained
13. (Original post by jit987)
Most of people here seems to be confused with the wording of that question 2.
I am confident that this is true:
It was 10 questions, so n=10 and 5 answers to each question, p=0.2. Therefore, X--B(10,0.2)
The student achieved 4 correct answers and this is 40% of the paper, but in theory it should be 20% (100*0.2). So he infact got MORE than normal. So the teacher said he was guessing, so we are testing whether or not p >0.2 because the student got 40% which is > than 20%.
.....X--B(10,0.2).....
H1: p = 0.2
Ho: p = >0.2
5% Significance level
Because we are testing its > than 20%, it is:
P(X>=4) = 1 - P(X<=3)....which came to around 0.12....this is >0.05(5%), so Reject H1, not significant and therefore there is sufficient evidence that the probability of of correctly answering is still 0.2. So the teacher's claim is CORRECT in saying that he was guessing.

I hope this can clear the confusion
Actually you should probably put "there is insufficient evidence that the teacher's claim was incorrect"
They still may have been guessing but this hypothesis test can not prove it at the 5% confidence interval.
14. (Original post by Gibbo81)
Actually you should probably put &quot;there is insufficient evidence that the teacher's claim was incorrect&quot;
They still may have been guessing but this hypothesis test can not prove it at the 5% confidence interval.
Yeh, in the paper I didn't put the exact wording as in that post. It was like "So there is insufficient evidence to reject Ho and sufficient evidence at 5% significance level that the teacher's claim is correct"
15. How many marks was question 2 worth? 6 or 7? Do i get marks for X-B(10,0.2) and do not reject H0? In which case i would get 2/6 right?

What did people get for the last 2? For 7c I got 0.478 and for 7d I got 0.467.
16. ignoring the changws to the grade boundaries

what are the percentages for
A
B
C
D
E
17. Can anyone tell me last question second last and last part??
18. has anyone got a link to the Exam paper? coz i actually cnt member the questions lol
19. You'll probably get the marks but it is important to know that just because you don't reject H0 does not mean that it is definitely true, just that this information does not suggest that it is false.
20. I'm going to post solutions as soon as I can

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