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January 6th, 2019, 06:46 AM   #1
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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.
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January 6th, 2019, 02:06 PM   #2
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Use a calculator to find the total of, say, the first 12 terms. What do you get?

The first 9 terms total $224 \frac{169}{256}$.
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January 6th, 2019, 08:07 PM   #3
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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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