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Math Help - simple question

  1. #1
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    simple question

    What is the sum of (2 to the n-1)/(3 to the n) where n goes from 1 to infinity?

    In other words what is the sum of 1/3 + 2/9 + 4/27 + 8/81 ...
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  2. #2
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    Quote Originally Posted by shadow1 View Post
    What is the sum of (2 to the n-1)/(3 to the n) where n goes from 1 to infinity?

    In other words what is the sum of 1/3 + 2/9 + 4/27 + 8/81 ...
    Hello,

    use the sum formula for infinite geometric series:

    \sum_1^{\infty}\left( \frac{2^{n-1}}{3^n} \right) = \sum_1^{\infty}\left( \frac{2^{n-1}}{3^n} \right) = \sum_1^{\infty}\left( \frac{1}{2} \cdot \left(\frac{2}{3} \right)^n \right) = \frac{\frac{1}{3}}{1-\frac{2}{3}} = 1
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  3. #3
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    Thanks earboth.

    So what you are saying is,
    if I have a pie and cut it into three pieces and ate one of them, I would have two one-third pieces left. Then if I cut each of those one-third pieces into three pieces and ate one, I would have four one-ninth pieces. And if I continue cutting each piece into threes and eating one of them, I will eventually eat the entire pie.
    Right?????
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  4. #4
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    Quote Originally Posted by shadow1 View Post
    Thanks earboth.

    So what you are saying is,
    if I have a pie and cut it into three pieces and ate one of them, I would have two one-third pieces left. Then if I cut each of those one-third pieces into three pieces and ate one, I would have four one-ninth pieces. And if I continue cutting each piece into threes and eating one of them, I will eventually eat the entire pie.
    Right?????
    Hello,

    that's it.

    I would recommend this method as a diet because you eat an infinite amount of pieces in an endless time and finally and actually you ate only one pizza
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