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January 6th, 2019, 06:46 AM  #1 
Member Joined: Aug 2018 From: Nigeria Posts: 73 Thanks: 2  Sequence&Series
Given the exponential sequence 3, 9/2, 27/4, ..., find the number of terms for its sum to be greater than 368.
Last edited by skipjack; January 6th, 2019 at 02:09 PM. 
January 6th, 2019, 02:06 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 21,105 Thanks: 2324 
Use a calculator to find the total of, say, the first 12 terms. What do you get? The first 9 terms total $224 \frac{169}{256}$. 
January 6th, 2019, 08:07 PM  #3 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1039 
a = 3 (1st term), m = 3/2 (common multiplier) Assume sum = 368 a(m^n  1) / (m  1) = 368 n = ~10.192 So 11. 

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