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Thread: Cumulative Sum

  1. #1
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    Cumulative Sum

    What would be the formula to come up with a cumulative sum? For example, x=100 and # periods=3 so that x+2x+3x=600. But I want to be able to change the # periods and x to calculate the cumulative sum. Thank you!
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  2. #2
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    Re: Cumulative Sum

    $x + 2x + \dots + n x = \displaystyle \sum \limits_{k=1}^n ~k x = x \sum \limits_{k=1}^n ~k = x \dfrac{n(n+1)}{2}$

    where $x$ is whatever you want and $n$ is what you're calling the number of periods.
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  3. #3
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    Re: Cumulative Sum

    Thank you so much!
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  4. #4
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    Re: Cumulative Sum

    That is, by the way, once you have factored out "x", an "arithmetic series": Arithmetic Series -- from Wolfram MathWorld.
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