Posted by **Greg** on Thursday, April 12, 2012 at 6:51pm.

What is the first term of a geometric series with a summation of 800, 4 terms and a common ratio of 3?

- Algebra 2 -
**Steve**, Friday, April 13, 2012 at 12:43pm
easy way:

1,3,9,27 adds to 40

800/40 = 20

so, 20,60,180,540

or,

a(1+r+r^2+r^3) = a(r^4-1)/(r-1) = a*80/2 = 40a

so, a = 800/40 = 20

- Algebra 2 -
**Greg**, Saturday, April 14, 2012 at 1:15pm
Thank you, I think I understand how to work it out now! That helped me out so much!

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