Find the sum of series 0.X + 0.XX + 0.XXX +… upto k terms

Given a series of k terms, where ‘X’ is any value between 0-9 and ‘k’ is any positive integer. The task is to find the sum of given series:

0.X + 0.XX + 0.XXX +… up to ‘k’ terms 

Examples: 

Input: x = 4 , k = 10
Output : 4.39506

Input: x = 9 , k = 20
Output: 19.8889

Explanation: 

C++

// C++ program for sum of the series
// 0.x,  0.xx, 0.xxx, ... upto k terms
#include <bits/stdc++.h>
using namespace std;

// function which return the sum of series
float sumOfSeries(int x, int k)
{
    return (float(x) / 81) * (9 * k - 1 + pow(10, (-1) * k));
}

// Driver code
int main()
{
    int x = 9;
    int k = 20;
    cout << sumOfSeries(x, k);

    return 0;
}

Java

// Java program for sum of the series
// 0.x,  0.xx, 0.xxx, ... upto k terms

public class GFG {

    // function which return the sum of series
    static float sumOfSeries(int x, int k)
    {
       float y = (float) (((float)(x) / 81) * (9 * k - 1 + Math.pow(10, (-1) * k)));
       return y ;
    }

    // Driver code
    public static void main (String args[]){
         int x = 9;
         int k = 20;
         System.out.println(sumOfSeries(x, k));
    }

// This code is contributed by ANKITRAI1
}

Python3

#Python3 program for sum of series
#0.x, 0.xx, 0.xxx, ... upto k terms

#function which return the sum of series
def sumOfSeries(x, k):

    return (float(x)/81) * (9 * k - 1 + 10**( (-1)*k ) )

#Driver code
if __name__=='__main__':
    x = 9
    k = 20
    print(sumOfSeries(x, k))
# This code is contributed by Shashank Sharma

C#

// C# program for sum of the series
// 0.x, 0.xx, 0.xxx, ... upto k terms
using System;

class GFG
{

// function which return
// the sum of series
static float sumOfSeries(int x, int k)
{
    float y = (float)(((float)(x) / 81) *
              (9 * k - 1 + Math.Pow(10, (-1) * k)));
    return y ;
}

// Driver code
public static void Main ()
{
    int x = 9;
    int k = 20;
    Console.Write(sumOfSeries(x, k));
}
}

// This code is contributed
// by ChitraNayal

PHP

<?php
// PHP program for sum of the series
// 0.x, 0.xx, 0.xxx, ... upto k terms

// function which return the
// sum of series
function sumOfSeries($x, $k)
{
    return (($x) / 81) * (9 * $k - 1 +
                      pow(10, (-1) * $k));
}

// Driver code
$x = 9;
$k = 20;
echo sumOfSeries($x, $k);

// This code is contributed
// by inder_verma.
?>

Javascript

<script>

// javascript program for sum of the series
// 0.x,  0.xx, 0.xxx, ... upto k terms

// function which return the sum of series
function sumOfSeries(x , k)
{
   var y =  (((x) / 81) * (9 * k - 1 + Math.pow(10, (-1) * k)));
   return y ;
}

// Driver code

 var x = 9;
 var k = 20;
 document.write(sumOfSeries(x, k));

// This code contributed by shikhasingrajput

</script>

Output:

19.8889

Time Complexity: O(logk), where k is the given integer.

Auxiliary Space: O(1), no extra space is required, so it is a constant.