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# Official Edexcel S3 thread Wednesday 20 May 2015 Morning [6691] watch

1. hi all i'm a bit stuck on 2b of June 2010 paper i did 60P-60J > 120 but the markscheme did 60J-60P>120...
2. https://869d950bf149eefd5cd2652b4001...%20Edexcel.pdf

Hi could someone please explain why a degree of freedom isnt used for estimating p? question number 6 thanks!
3. (Original post by ibbi1824)
hi all i'm a bit stuck on 2b of June 2010 paper i did 60P-60J > 120 but the markscheme did 60J-60P>120...
Remember whoever wins the race has the quicker time, that should hopefully help?
4. (Original post by ibbi1824)
hi all i'm a bit stuck on 2b of June 2010 paper i did 60P-60J > 120 but the markscheme did 60J-60P>120...
Philip beats James so J will be a bigger number than P, bigger by at least 2 mins.
5. (Original post by getback339)
https://869d950bf149eefd5cd2652b4001...%20Edexcel.pdf

Hi could someone please explain why a degree of freedom isnt used for estimating p? question number 6 thanks!
By saying "The gardener uses p=0.2" they imply that 0.2 was the known probability and it was not estimated. Hence you didn't use the estimated value that you calculated earlier but 0.2. That's a poorly done question though. It doesn't make it clear that this is the case.
6. How confindent on bias is everyone? is there any easy way of explaining it? theres only one example in the textbook and no questions on past papers (execpt international), its a bit of a dodgy subject for me. Thanks
7. Hi, please can someone explain 4 a on the s3 june 13 paper why when working out s2 they times by 50/49, I thought the formula what just:
{[sum of (fX2)]/(sum of f)}- xbar

ps sorry for the terrible formatting, i'm bad with computers :/
8. (Original post by pol234)
Hi, please can someone explain 4 a on the s3 june 13 paper why when working out s2 they times by 50/49, I thought the formula what just:
{[sum of (fX2)]/(sum of f)}- xbar

ps sorry for the terrible formatting, i'm bad with computers :/
its just the standad formula for unbiased varience, you multiply xbar^2 by n and divide by n-1.
9. Should I do any Solomon Papers for S3 as I have finished all the past papers?
10. june 14 r paper, q4 little help?

EDIT - DW, found my mistake, took my estimation away from Mew when i had to do it the other way around :/
11. (Original post by nayilgervinho)
Should I do any Solomon Papers for S3 as I have finished all the past papers?
YES! paper d and e are the best ones to do http://www.physicsandmathstutor.com/...rs/s3-solomon/
12. Thanks!
13. (Original post by tazza ma razza)
june 14 r paper, q4 little help?

EDIT - DW, found my mistake, took my estimation away from Mew when i had to do it the other way around :/
Good job, if only I had thumbs
14. It doesn't seem like the june 2014 IAL paper corresponds directly to the normal S3 paper, as they ask you to do stuff you've never had to do.
15. (Original post by Tazza'sNightmare)
Good job, if only I had thumbs
Cheers big man mean's a lot
16. (Original post by mmms95)
Do the older papers seem to be much shorter than the new ones (before June 2006)??? also for contingency tables, when you have to calculate expected freqencies do u show all you working out?? or just the formula written down once?
Yes i finish them in 40 minutes max which is useful but they're easier than the newer papers so be warned
17. Boom. 70 / 75 on the june 14 R paper

Just a question, IAL papers differ from R which differ from The Standard paper, which is harder?
18. For Solomon Paper D, q2b why is the answer: 19/20.2. A teacher gives each student in his class a list of 30 numbers. All the numbers have been generated at random by a computer from a normal distribution with a fixed mean and variance. The teacher tells the class that the variance of the distribution is 25 and asks each of them to calculate a 95% confidence interval based on their list of numbers. The sum of the numbers given to one student is 1419. (a) Find the confidence interval that should be obtained by this student. (5 marks) Assuming that all the students calculate their confidence intervals correctly, (b) state the proportion of the students you would expect to have a confidence interval that includes the true mean of the distribution, (1 mark) (c) explain why the probability of any one student’s confidence interval including the true mean is not 0.95 (1 mark)
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19. For spearman's rank, when finding the differences do you use negative values as well or all positive values?
20. (Original post by nayilgervinho)
For Solomon Paper D, q2b why is the answer: 19/20.2. A teacher gives each student in his class a list of 30 numbers. All the numbers have been generated at random by a computer from a normal distribution with a fixed mean and variance. The teacher tells the class that the variance of the distribution is 25 and asks each of them to calculate a 95% confidence interval based on their list of numbers. The sum of the numbers given to one student is 1419. (a) Find the confidence interval that should be obtained by this student. (5 marks) Assuming that all the students calculate their confidence intervals correctly, (b) state the proportion of the students you would expect to have a confidence interval that includes the true mean of the distribution, (1 mark) (c) explain why the probability of any one student’s confidence interval including the true mean is not 0.95 (1 mark)
Had a look, and I don't understand the mark scheme, says it either does or doesn't include the mean so probability is either 0 or 1, but surely that's the same for everything. The probability of anything is therefore 0 or 1 as it either does or doesnt happen? Dont think so.

Edit: just seen that you're on about b, sorry

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