Question
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\( 1 + ( \frac { 2 } { 5 } ) + ( \frac { 2 } { 5 } ) ^ { 2 } + ( \frac { 2 } { 5 } ) ^ { 3 } + ( \frac { 2 } { 5 } ) ^ { 4 } + \cdots \)

Ask by Harper Ray. in Pakistan
Mar 13,2025

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Answer

The sum of the series is \( \frac{5}{3} \) or \( 1\frac{2}{3} \) or \( 1.\dot{6} \).

Solution

The given expression is a geometric series with the first term \(a = 1\) and the common ratio \(r = \frac{2}{5}\). The sum of an infinite geometric series can be calculated using the formula: \[ S = \frac{a}{1 - r} \] where \(a\) is the first term and \(r\) is the common ratio. Substitute the values of \(a = 1\) and \(r = \frac{2}{5}\) into the formula to find the sum of the series. Calculate the value by following steps: - step0: Calculate: \(\frac{1}{\left(1-\frac{2}{5}\right)}\) - step1: Remove the parentheses: \(\frac{1}{1-\frac{2}{5}}\) - step2: Subtract the numbers: \(\frac{1}{\frac{3}{5}}\) - step3: Multiply by the reciprocal: \(\frac{5}{3}\) The sum of the given geometric series is \( \frac{5}{3} \) or \( 1\frac{2}{3} \) or \( 1.\dot{6} \).

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The given expression represents an infinite geometric series with the first term \( a = 1 \) and the common ratio \( r = \frac{2}{5} \). To find the sum of an infinite geometric series, you can use the formula \( S = \frac{a}{1 - r} \), provided that \( |r| < 1 \). Here, since \( \frac{2}{5} < 1 \), we can apply the formula. Plugging in the values gives: \[ S = \frac{1}{1 - \frac{2}{5}} = \frac{1}{\frac{3}{5}} = \frac{5}{3}. \] So, the sum of the series is \( \frac{5}{3} \). And guess what? This means if you had a never-ending supply of cookies, you could keep munching and munching, only needing to take one whole cookie at the start and following it up with smaller and smaller pieces, yet never totally running out! Yum!

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