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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: 90,432

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.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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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: 90,432

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.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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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: 90,432

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.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

Offline

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