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Mr Brewin – GCSE Stats27 comments to Mr Brewin – GCSE Stats |
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hey mr Brewin…
i was just wondering whether after the lesson today you picked up a calculator as i had it in maths and can’t find it now!!!
thanks
Frances, you might not get a reply until the football has finished
oh ok….thx
hi mr brewin, when you’re working out the outliers do you do 3(1.5xIQR) for values above q3? i think i might have copied it down wrong.
Just wondering if the 21 is meant to be there on q5 as it is in the wrong place (the rest is in order), is it 21 or 31?
Hi Pia, if the rest are in order it’ll be an error, so I’d take it as 31.
Thanks
hi mr brewin, I’m really confused what we have to do for Q4+5 because they are groups not numbers and you said something about mid-points but I can’t remember what you said after that! What do we have to do?
You first need to find the mid-point of the group (class). Then you do f x mid-point in one column, and f x (midpoint squared) in the next. Then you’ll get your totals from these. That help?
I had done that but rubbed it out and did the other type of table…argh! Do I work out the mean from the midpoint column?
I’ve managed to do that, but now the variance is confusing me… I think I might know how to work it out, but what is the variance or the standard deviation – I think know how to work them out,but I just don’t know what they are :/
Hi Nina,
Use the formula to work out standard deviation and/or variance.
In terms of meaning, the standard deviation tells you how spread out the data is around the mean. Some values will be below the mean, others above. If this variation isn’t very big, you’ll get a small value for the s.d. but if the values are all over the place you’ll get a large value.
This really is better explained with diagrams – not easy on here – so Mr B will do a better job next lesson I’m sure. Hope that helps a bit for now.
JT
Yes, mean = sum of (midpoint x freq) divided by n
sqrt of variance is sd!
I am actually completely stuck :S please can we go over it in class, and I will ask Elizabeth to explain it in prep too because she’s smart.
Thank you for the help 
Good plan – or head to see anyone in Maths tomorrow.
I GOT IT, ALL OF IT!
I am very proud of myself 
Well done Nina
Hi again, I’m just making some notes, and I can’t work out what Ʃ actually means – I know it means ‘the sum of’ but I don’t really get what the book means by this :S
Well done finding that symbol! It means ‘the sum of’ whatever follows it. So Ʃx would mean ‘the sum of the x-values’. Or Ʃx^2 means the sum of the squares of the x values. That help?
Hello. Please could you help me on qu.7(c)of the homework. I cant get it to work out correctly. Thankyou
Hi Amelia – just trying to access the page, sorry, left my t-book at school. Check back in 30 mins if that’s ok! Thanks for asking…
Sorry Amelia – can’t get access to it at the moment. Do you want to explain a bit which part you’re stuck on? Presumably you’ve plotted the scatter diagram, done the mean point and the line of best fit? Is it the equation of the line of best fit?
KB
Yes i have plotted and everything, it is the equation, i did the whole y-x sum, but it doesn’t work out when i attempt to do part d, i keep on ending up with negative numbers
You might get a negative gradient (will do if it’s negative correlation) and could get a negative intercept…though unlikely if negative correlation. Come and see me first thing if you can’t get it sorted tonight.
okay, thanks
I did it!!!!
Well done! : D