Algebra 2 series question

Question

Algebra 2 review question. Identify if the series is arithmetic or geometric. Then evaluate it

27+9+3+... s100

Answer 1

This is a geometric series with a common ratio of 1/3. The second term is a third of the first and the third is a third of the second so the series is

A(n) = A(1) x r^(n-1)

A(n) = 27(1/3)^(n-1)