Update: here’s a pseudo-equation for working out the median:
Where LCB=Lower Class Boundary, CW= Class Width, M.obs is the observation where the median is going to be, UC.Obs is the Observation at the Upper Class and LC.Obs is the same for Lower Class. Confused? Thought you would be!
Hope that helps!
Sorry didn’t get to post this last night. The latest slides on interpolation etc. are here.
The answers to the exercises from Chapter 2 so far are here:
All done for Weds please – do shout here if you need any help on the interpolation or anything else. Have a good w/e!
Ummm i think interpolation is beyond me.. I am trying but im confused.. :S
Hi Becky,
I don’t have an S1 here so can you explain exactly what you are trying to do and I’ll try and help you.
Mrs T
OK – come and see me Tues and we’ll sort it out. It seems complicated, but I’m sure after a few questions you’ll get the hang of it.
PS – any chance I could borrow your guitar again?! Mr Jope wants to practise something this week, and mine is still over in Chiswick.
haha yes thats fine Mr Brewin, do you want me to bring it in tomorrow?
Ah thanks Mrs Tibble but i don’t think i would be able to explain it well enough on the maths blog
i will just have to get help at school, thanks anyway
am i on the right blog now??
Be great if you could – ta!
Come and find me tomorrow and I’ll go over it again….
is it okay to use decimals in quadratic equations such as “completing the square”?
Or is it more beneficial for one to use fractions?
Easier to use fractions: they square and square-root more easily
Are you right-handed?
wait.. I’m really confused are we supposed to use that other equation instead of the one you gave us already oin class??? or are you just giving us options..
Think he’s giving you options Grace. That one above looks scary – I’d choose tea if I was you!!
it really does look scarey doesn’t it!!
I’ve used the other one anyway so it’s all alright..
I’ll just write that other one in my book to look clever..
lol
Sure it’s OK grace… I did it in a moment of madness when Becky said people hadn’t got it!
We’ll go over it tomorrow and try to make sense of it!
umm.. this is embarassing… i dont understand the coding questions on the mixed exercise, im not sure what it is asking me to do
This is Q6 on 2F, right?
It’s given you the coded mean, and the way the data was coded. It’s asking you to work out what the actual mean is – which you do by reversing the coding. OK?
1) yes Mrs Tibble, i am right-handed
2) Mr Brewin, on the topic of interpolation:
e.g. if Q1 = 389.083recurring
can i round it up to 389kg or do i leave some decimal places???
well i think i have done question 6, it just seems to be question 5 that confuses me.
Dex: yes, 3sf is fine. 4 if you like.
Bex: For 5, the coding is asking you to subtract 7 from each observation, then divide by 80. POINTLESS I know, but when you’ve done that, you’ll get 10, 12, 8, 2, 2.5, 8.5 (in my head). Find the mean of these, then un-code to find the mean of original observations. Yes, I know, it’d be much quicker to tap the data in to your calc as it is!
fanx
and actually it is 9 not 8
and what do you mean by un-code
so it’ll be: mean of those values(y)=(x-7)/80
and then work that out???
Yeah, do the mean of those simpler values… then x 80 and + 7
okay
sorry to keep bothering you but i have another queztion
on q7 (the one with the table with group A and group B….continuous data question)
do i use the mid-class value, etc? just to be sure
Yes. Mid-class x freq… sum those.
thanx
can i ask a rather unrelated question?
that is kind of related
but not depending on the way you look at it
anyway, i digress
what is the average grades achieved at AS level ?
average? see what i did there? ha! really now.
By whom and in what subject??
for maths
errrrrm mr brewin and mr burford?
just curious ^^
ALSO actual maths help needed
cumulative frequency goes as such:
group 0 CF = 25
group 1 CF = 35
if Q1 = 25 that goes in group 0. . . . right? or wrong . . . ? aaaah !!
wait – do we even need to know if it goes into which group if youre trying to find out the interquartile range?
this is so confusing.
When you say CF=25 do you mean there are 25 values in group 0? (Hate this type-face which shrinks the zeros!!)
Maths grades depend on the person sitting the paper Sandrinne! Haven’t you worked that one out yet?
yuppp there are 25 values in group 0 [yeah me too,
o and 0 have no difference !!!]
and yeah i suppose i realised
*sigh*
Well done!
:O i hope that wasnt sarcasm
on a more important note, you know the special homework?
actually its ok got it sorted.
for any teacher available
with an equation
e.g. x+y=11 and xy=30
is it correct for me to rearrange the first like so…y=11-x. Then to substitute that into xy=30
so it’ll look like so… x(11-x)=30
and then work out??
Yes, that’s fine
thanx Miss
also 2x+y=1 and x2 +y2=1
i can do the rearrangement and the substitution but i cant factorize it
ive gotten to (5x ) (x ) but i dont kno what to do with it
You see those simultaneous questions that Deola was asking about.. I’ve been finding them difficlut.. I just can’t seem to make them work properly
I’m guessing that this is too late but…
Deola:
Is your question as follows?
2x+y=1 and x^2 + y^2 = 1
If so then from the first y = 1-2x
Now sub this into the second one, giving
x^2 + (1-2x)^2 = 1
Expand giving
x^2 + 1 – 4x +4x^2 = 1
So now tidy it up and get
5x^2 – 4x + 1 = 1
Subtract 1. I think you got to about here.
5x^2 – 4x = 0
Methods for solving from here include factorising or formula or difference between squares. The choice is yours.
Hope that this helps.
MW
for mr brewins *special homework*im getting stuck because say if the coded mean of employee’s annual earnings (£x) for a store is 18, the code that was used was
y= x – 720 (over) 1000
how would you work out the uncoded mean earnings? but just putting in 18 as x? ?
or you make y 18
got it all
OK now? Yeah – you put 18 as y, then work back.
And sorry – was out last night. And it wasn’t sarcasm! It was actually just showing some parents how the blog worked
Well done anyway!
hahah well phew !
ok LAST QUESTION
after two hours of my life slaving on this homework
you knw the last question how would you work it out when another batch of 12 batteries is found to have an estimated mean lifteim of 22,.3 hours [i got the mean for all 80 batteries as 20.6]
do you do something like divide 12 by 22.3 ? or ? aaah i dont know !
OK, hope this isn’t too late…. You’ve got to combine the two data sets. The total is (22.3 x 12) + (20.6 x 80)…. then you divide that total by 100 to get the combined mean. OK?
ok thankyooou
got 19.156
well hope thats right
Hmmm….. should be 20.8 I think, but don’t worry about it – we’ll go over it.
Hi,
Umm… i need to check a few things with u quickyly:
1) calculating the median…can u just do n/2 or must i always use n+1/2?
2) class boundaries: if the classes are like, 30-35, 35-40. would the class boundaries just be 30 and 35?
Hi Deola,
1) (n+1)/2 which locates the middle item for an odd number of items, and halfway between the middle two for an even number of items.
eg if there are 50 pieces of data, there are 2 middle items – nos 25 and 26 – and the median is hafway between them at position 25.5 (which is half of 51 not 50)
2) Yes
Tea Lady
thanx Mrs T,
so basically i always use n+1/2
but if there are 50 pieces of data, isnt it simpler to just divide it by 2 and get 25….ooooooh i understand now why i cant do that
okaii thankyou
also…with stem and leaf diagrams, when asked to find the median: if we do 15+1/2=15.5. Does one round up to 16 (like with discrete data)or leave it at 15.5 and then read it off the table?
Deola, if there are 15 leaves, then the middle one is number 8!
(15 + 1) / 2 is not the same as 15 + 1/2!!!!
If the two middle items are the same, then that is the value of the median; if they are different, take their mean.
ooh i get it
fanx