How do you find $S_n$ for the geometric series $a_1=72$ , r=1/3, n=7?

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Answer 1 · 2017-11-19T12:30:40

$S_n ~~ 107.95$

$a_1=72, r=1/3 ,n=7 , S_n=?$

Summation formula: $S_n= a_1*(1-r^n)/(1-r)$

$= 72*{1-(1/3)^7)/(1-1/3)~~ 107.95 (2dp)$

$S_n ~~ 107.95 (2dp)$ [Ans]

How do you find S_nS_n for the geometric series a_1=72a_1=72, r=1/3, n=7?