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Homework Help: Sum of a geometric series up to infinity

  1. Mar 23, 2012 #1
    1. The problem statement, all variables and given/known data
    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?

    2. Relevant equations

    3. 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
  2. jcsd
  3. Mar 23, 2012 #2


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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Alekz! Welcome to PF! :smile:

    Start by writing the nth term as a function of n :wink:
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