<PRE><B>Question 140835</B>
calculate the 20th partial sum for 6400,1600,400,100,25...?
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You have a geometric sequence with r = (1/4), and a(1)=6400.
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S(20) = 6400[r^n -1]/[r-1]
S(20) = 6400[(1/4)^20 -1]/[-3/4]
S(20) = 8533.3333...
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Cheers,
Stan H.
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