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# AQA Statistics GCSE exam June 18th 2012

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1. Hi guys,

I was just wondering how everyone is getting on with Statistics revision, and how we all find the actual exam on the day
2. Well I don't really know what else to revise for I was three marks off an A* in the mock, but now I think I know where I went wrong, so I'm just practising how to do weighted index numbers, as these are my weakness. Do you know if we have to know about how to calculate crude birth rate/death rates etc. It was on the old syllabus but I'm worried it's going to come up and I haven't revised it
Sorry for the essay
3. Hi everyone, I've just been going through as many past papers as I can. I've also made a list of all the common questions that tend to come up which is good because the answers are literally the same each time in mark schemes. I've got Geography that day in the morning as well sadly! So my efforts are being shared on these two this weekend. Other than that, what do you think will come up? The standard deviation, spearman's rank, average seasonal variation and the wordy ones are a must.
4. Is seasonal variation related to moving averages?
5. I really want an A* for this exam because statistics has quite a major part in my aspired job. Though, I really don't know much of the syllabus and I could do with some help. I have the weekend to cram, tbh. I know how I would do some basic calculations, along with standard deviation and outliers. However, not too sure on Spearman's Rank or the other aspects.. Please could someone kindly explain this to me?
6. spearman's rank. Rank the results, for example if two jugde's rank a performance, then you find the different then difference squared, then the total of d square. Then apply it to the given equation, 1-6[sum of difference squared]/n(n squared-1) n is the number of rankings
7. It gives u that on the paper anyway. What are these wordy questions involve, their my weak point.
8. okay.. can anyone explain question 8b on the practice paper 43101H? thanks
9. (Original post by -Ben)
okay.. can anyone explain question 8b on the practice paper 43101H? thanks
If we are looking at the June 2011 series then the question is to do with chain base index numbers.
8)b) Answer is 2007
Because if you minus the chain base index number from it's index (100) you get the smallest value (2.3) which means 2007 had the smallest increase in insurance cost.

P.S. Grade boundaries for this exam where really low . It was 68% for an A* and 53% for an A... And the paper was out of 100 so a percentage isn't hard to figure out
10. sorry. I didn't mean that question. I meant the one on the practice paper that says: Assuming the times to withdraw money are normally distributed, work out their limits within which 95% of these times will fall. Thanks for the reply, though
11. (Original post by -Ben)
sorry. I didn't mean that question. I meant the one on the practice paper that says: Assuming the times to withdraw money are normally distributed, work out their limits within which 95% of these times will fall. Thanks for the reply, though
Could you link me the practice paper please?
12. PP:

http://www.school-portal.co.uk/Group...urceId=4563043

Would have linked earlier, but I couldn't find it.

MS:
http://sidcotmaths.wikispaces.com/fi...ark+scheme.pdf

Thanks!
Are there any revision resources I could use also?
13. Ah, ok now i Think i can realistically answer your question. You need to know three things about normally distributed graphs:
In the range of +- 1 S.D (Standard Deviation), 68% of all data lies in this region.
In the range of +- 2 S.D, 95% of all the data lies within this region
And In the range of +- 3 S.D, 99.8% of all data lies within this range.

For this question the 95% is important which is the +- 2 S.D. From the previous question you know the mean which is 61 seconds and you need to find out what 1 S.D is by doing the formula and then times that by 2 to get the range of 2 S.D. So:
Root of: 450556.8/120 - 61^2 This will give you the S.D
The answer to that is 5.8 seconds which is 1 S.D.
Times that by 2 to get 2 S.D which this question requires which is 11.6 and add 11.6 to the mean to get the upper boundary and minus the 11.6 from the mean (61) to get the lower boundary. And bingo, your answer!
61 - 11.6 = 49.4
61 + 11.6 = 72.6

Hope that helps then!

EDIT: Must admit though, it doesn't give you a lot of room to work with... But anyway I hope i helped, any other questions and i will try to help
14. Oh one other thing, you wouldn't happen to know the grade boundaries for the practice paper would you? Plan on doing this paper tomorrow
15. Thank you for that! I can do it now, but if a similar question came up I'm not sure if I would be able to remember the process :P And I do not have access to the grade boundary, sorry
16. (Original post by -Ben)
Thank you for that! I can do it now, but if a similar question came up I'm not sure if I would be able to remember the process :P And I do not have access to the grade boundary, sorry
Just remember the appearance of a normal distribution (That is the KEY word in the question) and remember that +-1 S.D is 68% of data, +-2 S.D is 95% and +-3 S.D is 99.8% of all the data. Those value you HAVE to remember, it will probably come up. Glad I could help.
17. Thanks. Not too confident on these topics: moving averages (i think),the z chart thing (how to plot them), how to calculate freq density, and grouped and grouped mean frequency distribution. Plus frequency distributions in general, lolHelp would be greatly appreciated (:
18. (Original post by -Ben)
Thanks. Not too confident on these topics: moving averages (i think),the z chart thing (how to plot them), how to calculate freq density, and grouped and grouped mean frequency distribution. Plus frequency distributions in general, lolHelp would be greatly appreciated (:
Ok i will try to help.
Moving averages:
This is the thing where you calculate the average with the first 4 values and then continue calculating averages while moving across 1 value at a time E.G:

Year: 2001 - 2002 - 2003 - 2004 - 2005 - 2006 - 2007
Price: £20 - £22 - £26 - £29 - £31 - £34 - X

Here the average on the first 4 values is (20+22+26+29)/4 which is 24.25
Next 4 value average: (22+26+29+31)/4 = 27
Next 4 value average: (26+29+31+34)/4 = 30
Next 4 value average: This is where the question is usually in an exam paper. Predict a value for the price in 2007 using moving averages.
Now to do this you look at the pattern of existing averages you have calculated above and see if you have a pattern. You can see the value is roughly moving up 3 each time so the next moving average should equal 33.
Then: (29+31+34+X)/4 = 33 .... Find X
= (94 + X)/4 = 33 X=38 So we have a value for 2007 which is 38!
NOTE: Just remember the 4 values you have to average then move along 1 value and calculate the next average (It doesn't have to be 4 values, just remain constant when calculating the average such as you can use 6 values to average, just use 6 all along the averages.)

Z-Charts:
These are lovely...
Ok, first off, here is a link to an example z-chart to reference to:
http://peltiertech.com/images/2010-04/ZchartYr3.png
So, look at that and first off, the bottom line is a simple plot business, (Referring to the example) Plot the month and the sales along the bottom line.
The second middle diagonal line is the cumulative frequency of the sales which i'm sure you know how to do which goes right to the top and joins on nicely to the yearly line which i will explain.
The top line is 'Rolling 12 month total'. You won't be asked to calculate this, it will give it to you in the exam, you just have to plot it but in simple terms, it is the Long-term improvement/decline as it uses data from a long time ago (Usually a year previous). It is the rolling year total so it is E.G. Previous March to current March, then previous april to current april so without previous measurements, you cannot make this, but you can plot it!
For the understanding of it: Using the example you can see (From the bottom line) the sales have been quite consistent over the year but in the long term they have been experiencing a loss of money.

The rest I will type out tommorow in detail, Damn tired
19. Thanks for the explanations so far! Very helpful ))
20. Someone help me ! I am not prepared for this exam ! My teacher said he didn't want to teach us anything on this topic because we have other exams and it doesn't matter if we fail. Does anyone know the basic things I need to know to get at least a C?

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