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Math Help - Arithmetic Sequence - Series Questions

  1. #1
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    Arithmetic Sequence - Series Questions

    How many terms for the arithmetic sequence {-3,2,7,...} must be added together for the sum of the series to be 116? - SOLVED, Thanks pickslides!


    Also;


    Find the least value of n for which Sn>10000 for the sequence {3,6,12...}

    Finally

    A ball is dropped from a height of eight feet. The ball bounces to 80% of it's previous height of each bounce. How high (to the nearest tenth of a foot) does the ball bounce on the fifth bounce?


    I know I can logically solve some of these problems with logic, but I need to do it arithmetically. I don't necessarily need these solved, just the appropriate process to go about solving them.
    Last edited by Diesal; January 12th 2012 at 08:55 PM.
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  2. #2
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    Re: Arithmetic Sequence - Series Questions

    For the first one, 116 = \frac{n}{2}(2a+(n-1)d)

    What is a (the first term) and d (the common difference) in your sequence?

    Once you know then solve for n.
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  3. #3
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    Re: Arithmetic Sequence - Series Questions

    I get to 116=n/2(5n-11) and I feel like I'm going to end up factoring a quadratic, is that correct?
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  4. #4
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    Re: Arithmetic Sequence - Series Questions

    I have the same feeling.
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  5. #5
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    Re: Arithmetic Sequence - Series Questions

    Alright, so n=8 and n=-29/5. I filled 8 in for n and got 116. You are a great human being for taking the time to help me. Thank you so much for the first answer!
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