Question

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

Answer 1

`S_n ~~ 107.95`

Explanation:

`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]