Sum of a geometric series up to infinity

[Alekz]

Homework Statement

A geometric series had first term 54 and 4th term 2.
(i) What is the common ratio?
(ii) Find the sum to infinity of the series.
(iii) After how many terms is the sum of the series greater than 99% of the sum to infinity?

Homework Equations

N/A

The Attempt at a Solution

(i) Is obviously 1/3 (54,18,6,2...)
I've no idea how to attempt ii or iii, if someone could explain this I'd be grateful

 

[tiny-tim]

Welcome to PF!

Hi Alekz! Welcome to PF!

Start by writing the nth term as a function of n