Furthermaths | Revision Server | Page 1

empty barn Dec 13, 2023, 5:06 PM

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try and write the sum of all the masses of the marbles in sigma notation

terse heath Dec 13, 2023, 5:11 PM

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empty barn try and write the sum of all the masses of the marbles in sigma notation

you know for parta) isnt the sequence infinite so how do i calculate mean

empty barn Dec 13, 2023, 5:13 PM

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its not infinite bc they said it contains n marbles

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ur finding the mean in terms of n

terse heath Dec 13, 2023, 5:17 PM

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so if each subsequent term is +3 starting from 10grams , therefore the sequence will be 10, 13, 16, ... , n+3 etc so do i have to form some expression involving mean formula or nth term?

empty barn Dec 13, 2023, 5:18 PM

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have u studied the chapter on series

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in further maths core pure

terse heath Dec 13, 2023, 5:18 PM

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not good with worded qs

empty barn Dec 13, 2023, 5:19 PM

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thats fine but r u familiar w the non-worded questions

terse heath Dec 13, 2023, 5:19 PM

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yh

empty barn Dec 13, 2023, 5:19 PM

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also r u in y11

terse heath Dec 13, 2023, 5:19 PM

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should be 12

empty barn Dec 13, 2023, 5:19 PM

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oh alr

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ite so mean mass is what i get if i add up all the masses and divide by the number of marbles right

terse heath Dec 13, 2023, 5:20 PM

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yh

empty barn Dec 13, 2023, 5:20 PM

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number of marbles is easy to get bc thats just n

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so we have to worry about the sum of marbles

empty barn Dec 13, 2023, 5:21 PM

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terse heath so if each subsequent term is +3 starting from 10grams , therefore the sequence ...

as u said the series will be 10 + 13 + 16 + …

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so whats the nth term of that series

terse heath Dec 13, 2023, 5:21 PM

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3n+7

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or r

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doesnt that say in qs

empty barn Dec 13, 2023, 5:22 PM

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yeah

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so how would u write the sum in sigma notation

terse heath Dec 13, 2023, 5:23 PM

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n sigma r=1 3r+7

empty barn Dec 13, 2023, 5:23 PM

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yeah

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and then u can use the standard summation formulae to simplfy that

terse heath Dec 13, 2023, 5:31 PM

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have i done something wrong bc i dk why im ending up with an extra n

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i did 3sigma r + 7sigma

empty barn Dec 13, 2023, 5:32 PM

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yeah

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what have u jus worked out?

terse heath Dec 13, 2023, 5:32 PM

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but dont that make 1/2n(3n+17)

empty barn Dec 13, 2023, 5:33 PM

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wait could u send ur working

terse heath Dec 13, 2023, 5:33 PM

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yh let me write it more neater

empty barn Dec 13, 2023, 5:34 PM

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u dont have to i just wanna check one thing

terse heath Dec 13, 2023, 5:35 PM

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did i miss something

terse heath Dec 13, 2023, 5:39 PM

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empty barn u dont have to i just wanna check one thing

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empty barn Dec 13, 2023, 5:39 PM

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nope

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thats correct

terse heath Dec 13, 2023, 5:39 PM

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oh

empty barn Dec 13, 2023, 5:39 PM

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but what is that

terse heath Dec 13, 2023, 5:39 PM

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i have to dvivde by n

empty barn Dec 13, 2023, 5:40 PM

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yeah

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for the mean

terse heath Dec 13, 2023, 5:40 PM

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forgot mean

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my bad

empty barn Dec 13, 2023, 5:40 PM

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nws

terse heath Dec 13, 2023, 5:53 PM

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empty barn nws

btw i tried attempting partb and is it right for me to use standard deviarion formula by calculating mean of the 85 balls by just substituting 85 into the expression from parta?

empty barn Dec 13, 2023, 5:53 PM

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yh thatd help u to find the mean for the 85 but theres still more calculations needed to find the s.d

terse heath Dec 13, 2023, 5:54 PM

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u know for the sigmax^2 part of standard deviation

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isnt it 208353?

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/85

empty barn Dec 13, 2023, 5:54 PM

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how did u work it out

terse heath Dec 13, 2023, 5:55 PM

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by 1^2 ... up to 85?

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or thats wrong?

empty barn Dec 13, 2023, 5:55 PM

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ur gonna be adding up all the masses squared

terse heath Dec 13, 2023, 5:55 PM

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oh

empty barn Dec 13, 2023, 5:55 PM

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so 10^2 + 13^2 + 16^2 …

terse heath Dec 13, 2023, 5:57 PM

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how would that be written on cal?

terse heath Dec 13, 2023, 6:00 PM

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empty barn so 10^2 + 13^2 + 16^2 …

would it be 2032690 then?

empty barn Dec 13, 2023, 6:00 PM

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i havent done it myself but id think they want u to work out the sum instead of using ur calculator

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its gonna be the sum from 1 to 85 of (3r + 7)^2

terse heath Dec 13, 2023, 6:00 PM

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yh i wrote that on cal

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letme try doing it through working it out

terse heath Dec 13, 2023, 6:05 PM

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empty barn its gonna be the sum from 1 to 85 of (3r + 7)^2

i got 3sqrt602 can u pls confirm

empty barn Dec 13, 2023, 6:10 PM

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sorry was eating

empty barn Dec 13, 2023, 6:10 PM

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terse heath i got 3sqrt602 can u pls confirm

couuld u send ur working

terse heath Dec 13, 2023, 6:13 PM

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terse heath Dec 13, 2023, 6:14 PM

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empty barn couuld u send ur working

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empty barn Dec 13, 2023, 6:18 PM

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all the calculations look correct

empty barn Dec 13, 2023, 6:19 PM

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terse heath

it does say to give the answer to 1dp tho

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