LilyMQ
  • LilyMQ
What is the sum of a 23-term arithmetic sequence where the first term is 9 and the last term is 119?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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LilyMQ
  • LilyMQ
Is it 1472? That's what I got
Jhannybean
  • Jhannybean
First define what an arithmetic sum is.
SolomonZelman
  • SolomonZelman
i think you are a little off

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More answers

LilyMQ
  • LilyMQ
So it's wrong?
SolomonZelman
  • SolomonZelman
\(\large\color{black}{ \displaystyle a_9=9 }\) \(\large\color{black}{ \displaystyle a_{23}=119 }\) \(\large\color{black}{ \displaystyle {\rm S}_{23-9}=\frac{\left(a_9+a_{23}\right)}{2} \times(23-9) }\) \(\large\color{black}{ \displaystyle {\rm S}_{23-9}=\frac{\left(9+199\right)}{2} \times(23-9) }\)
SolomonZelman
  • SolomonZelman
where 23-9 is the number of terms, and the first fraction is the average term
LilyMQ
  • LilyMQ
is it 1456?
Jhannybean
  • Jhannybean
That is, \[\large S_n=\frac{n(a_1+a_n)}{2}\]To find \(a_n\) we need to use an arithmetic sequence, \(a_n = a_1 +(n-1)d\)
LilyMQ
  • LilyMQ
okay
SolomonZelman
  • SolomonZelman
we know the 23rd term, Jhanny....
Jhannybean
  • Jhannybean
Yeah I just reread it haha
SolomonZelman
  • SolomonZelman
i think all you need is last+first term \(a_{23}\) and \(a_9\) in this case....
SolomonZelman
  • SolomonZelman
alright....
SolomonZelman
  • SolomonZelman
1456 is right....
SolomonZelman
  • SolomonZelman
1456 apples, jk
Jhannybean
  • Jhannybean
but whats with the multiplication?
LilyMQ
  • LilyMQ
then what?
SolomonZelman
  • SolomonZelman
multiplication ?
SolomonZelman
  • SolomonZelman
(9+199)÷2 => the average term 23-9 = number of terms (9+199)÷2 • (23-9) = the sum of all terms together
Jhannybean
  • Jhannybean
\[\large S_{23} = \frac{23(9+119)}{2}\]
SolomonZelman
  • SolomonZelman
not 23
SolomonZelman
  • SolomonZelman
you don't add the terms before \(a_9|)
SolomonZelman
  • SolomonZelman
oh, my bad
LilyMQ
  • LilyMQ
so it is 1472?
SolomonZelman
  • SolomonZelman
what the hell am I saying....Jhanny, i am a laborer before thee
Jhannybean
  • Jhannybean
You wrote 199 instead of 119 O_o
SolomonZelman
  • SolomonZelman
i read \(a_9\) with my blind eyes.
Jhannybean
  • Jhannybean
and @LilyMQ I have no idea. No calculator here, just helping you understand the format :)
SolomonZelman
  • SolomonZelman
9 is the 1st term... then it is completely off....
SolomonZelman
  • SolomonZelman
(9+199)÷2 => the average term 23 = number of terms (9+199)÷2 • 23 = the sum of all terms together
SolomonZelman
  • SolomonZelman
sorry for my mistake.
LilyMQ
  • LilyMQ
oh, so it's 2392?
SolomonZelman
  • SolomonZelman
yes, this is correct
SolomonZelman
  • SolomonZelman
and this time, it is correct for real:D
LilyMQ
  • LilyMQ
Yay. Okay thanks guys!
LilyMQ
  • LilyMQ
Wait wait
LilyMQ
  • LilyMQ
That doesn't make sense. These are the options 1,219 1,472 1,725 1,978
LilyMQ
  • LilyMQ
HELPP
SolomonZelman
  • SolomonZelman
the first term is 9 the last (i.e. 23rd) term is 199 are you sure about this information ?
LilyMQ
  • LilyMQ
What is the sum of a 23-term arithmetic sequence where the first term is 9 and the last term is 119?
LilyMQ
  • LilyMQ
119 not 199 lol
SolomonZelman
  • SolomonZelman
oops my fault again, i will try to, if i can, to refrain from my mistake
SolomonZelman
  • SolomonZelman
i will re-correct my post again. tnx for catching the err.
LilyMQ
  • LilyMQ
haha it's okay
SolomonZelman
  • SolomonZelman
(9+119)÷2 => the average term 23 = number of terms (9+119)÷2 • 23 = the sum of all terms together
SolomonZelman
  • SolomonZelman
u were correct initially....
LilyMQ
  • LilyMQ
o
LilyMQ
  • LilyMQ
okay thank you lol
SolomonZelman
  • SolomonZelman
You are like :O and I am like Oh..... my fault, lol
SolomonZelman
  • SolomonZelman
thank YOU for catching it.... with me you would have gone into the forest of unnecessary wonders.
SolomonZelman
  • SolomonZelman
Good luck:)

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