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Edexcel S1 - 15th June, 2016 [Exam Discussion]

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Can someone please tell me how to round numbers for the S1 module? I never know whether to round to 3sf or 1dp unless it's stated in the question especially with questions about the regression model e.g. y = a + bx
Original post by Philip-flop
Can someone please tell me how to round numbers for the S1 module? I never know whether to round to 3sf or 1dp unless it's stated in the question especially with questions about the regression model e.g. y = a + bx


Have a look at past papers :tongue: I'd answer myself but I do not know. :hide:

A look at one paper seems to suggest that most stuff just needs to round to some correct value, and with the regression stuff it's 3 sf. Would suggest looking at other papers though.
(edited 7 years ago)
How is the median 54 and not 53 for the Year 11 class?
Original post by Philip-flop
Can someone please tell me how to round numbers for the S1 module? I never know whether to round to 3sf or 1dp unless it's stated in the question especially with questions about the regression model e.g. y = a + bx


Give your final answer to 3sf unless stated otherwise or if it's a number like, 28702.3452...., then 2 decimal place should be sufficient.
During intermediate stages, use unrounded values, by using calculator memory.
Original post by NotNotBatman
Give your final answer to 3sf unless stated otherwise or if it's a number like, 28702.3452...., then 2 decimal place should be sufficient.
During intermediate stages, use unrounded values, by using calculator memory.


Thank you soooooo much! That has helped me a lot! :smile:
Original post by target21859
How is the median 54 and not 53 for the Year 11 class?


They've most likely used (n+1)/2.. why, I cannot tell you, but that gives you 16.5 and then you pick the number inbetween 16 and 17.
Original post by SeanFM
They've most likely used (n+1)/2.. why, I cannot tell you, but that gives you 16.5 and then you pick the number inbetween 16 and 17.


I get that but there is no value between 53 and 55. There is no 54 push ups value. Also I thought you found the median as n/2 then round up to nearest integer if the data is discrete.
Original post by target21859
I get that but there is no value between 53 and 55. There is no 54 push ups value. Also I thought you found the median as n/2 then round up to nearest integer if the data is discrete.


http://www.bbc.co.uk/schools/gcsebitesize/maths/statistics/measuresofaveragerev3.shtml

I'm not trying to be funny or offensive, that is genuinely useful :tongue:
Original post by SeanFM
http://www.bbc.co.uk/schools/gcsebitesize/maths/statistics/measuresofaveragerev3.shtml

I'm not trying to be funny or offensive, that is genuinely useful :tongue:


None taken xD Thanks that was useful. Good old gcse maths.
Resisting this and have done no revision at all along with no paper papers and I also have bio unit 4 the day before and Chem unit 4 the day after so I'll be lucky if I beat the c I got last year


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Avatar for candol
candol
7
Original post by target21859
How is the median 54 and not 53 for the Year 11 class?


I've seen mark schemes before where they have accepted either version of the median . Eg interpolation to find median
Does anyone know where I can find good notes on the effects of coding, especially when the data is coded when you are working out regression lines.
Reply 152
Avatar for imran_
imran_
2
Original post by KloppOClock
Does anyone know where I can find good notes on the effects of coding, especially when the data is coded when you are working out regression lines.


Mean: everything affects it e.g adding subtracting multiplying and dividing

standard deviation: only multiplying and dividing affects it

PMMC: NOTHING. Affects it


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When to use these three different types of skewness tests?

Q2-Q1 : Q3-Q2

Mode>Median>Mean

3(Mean-Median) divided by standard deviation



also what is the a for in Var(a+bx)
(edited 7 years ago)
Original post by KloppOClock
When to use these three different types of skewness tests?

Q2-Q1 : Q3-Q2

Mode>Median>Mean

3(Mean-Median) divided by standard deviation





also what is the a for in Var(a+bx)


Normally when they want you to evaluate skewness using 3(Mean-Median)/SD they will tell you in the question. You use the other metrics if they don't tell you to use that equation

The A doesn't affect the value of the variance because only multiplying/dividing affects it
Original post by CrazyFool229
Normally when they want you to evaluate skewness using 3(Mean-Median)/SD they will tell you in the question. You use the other metrics if they don't tell you to use that equation

The A doesn't affect the value of the variance because only multiplying/dividing affects it


i know but why is the a there in the first place?
Original post by KloppOClock
i know but why is the a there in the first place?


Because when coding the equation might have a constant
Original post by CrazyFool229
Because when coding the equation might have a constant


ok thanks
Original post by KloppOClock
When to use these three different types of skewness tests?

Q2-Q1 : Q3-Q2

Mode>Median>Mean

3(Mean-Median) divided by standard deviation



also what is the a for in Var(a+bx)


The question will usually ask for the skewness with a reason. This usually is a later part of the question and so you'd use your previous answers to answer this. It depends which one you use according to what you have.

Also the a in Var(a+bx) has no effect
is like a solid 4 full days enough to cover stats, hoping for an A any suggestions of what to do?

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