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#1 2013-06-12 14:54:18

Nikster
Member
Registered: 2013-06-12
Posts: 3

Arithmetic Series - Finding Terms when given two sums

Find the first five terms of an arithmetic series with S10 = 210 and S20 = 820
S= Sum

Last edited by Nikster (2013-06-12 14:54:47)

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#2 2013-06-12 15:12:04

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,168

Re: Arithmetic Series - Finding Terms when given two sums

Hi;

I am getting:

3, 7, 11, 15, 19, ...


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#3 2013-06-12 15:43:38

Nikster
Member
Registered: 2013-06-12
Posts: 3

Re: Arithmetic Series - Finding Terms when given two sums

I missed this class on how you do this. What process did you go through to get these numbers?

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#4 2013-06-12 15:51:07

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,168

Re: Arithmetic Series - Finding Terms when given two sums

I solved 2 equations simultaneously: This is the formula for an artihmetic sum.

we have

this means we have 2 n's for equation1. With 2 n's we can get a1 ( the first term ) and d ( the distance between each term ). We have the 2 n's they are n =10 and n = 20.

Substituting into 1:


Clean em up:

Solving:

a1 = 3
d = 4

Can you finish up now?


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#5 2013-06-12 16:07:44

Nikster
Member
Registered: 2013-06-12
Posts: 3

Re: Arithmetic Series - Finding Terms when given two sums

I understand! Thank you so much!

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#6 2013-06-12 16:11:20

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,168

Re: Arithmetic Series - Finding Terms when given two sums

Hi Nikster;

Your welcome and welcome to the forum!


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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