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Math Help - Geometric sums and series.

  1. #1
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    Question Geometric sums and series.

    Find the sum accurate to 1 decimal place, of the 20 terms of the geometric series having T1=15, and T2=20 answer is 14145.2

    I do r= 20/15
    a= 15
    n=20

    so 15((20/15)^20-1) over (20/15)-1

    and I get 14187?

    I dont totally understand the question, what is it Im doing wrong?
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  2. #2
    MHF Contributor
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    Hi

    You are doing nothing wrong except the calculus itself

    15\cdot \frac{\left(\frac{20}{15}\right)^{20}-1}{\frac{20}{15}-1} = 14145.2
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  3. #3
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    I got it thanks..
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