Math Problem Statement

Calculate the sum of the infinite repeating decimal series: 1 + 3/10 + 6/10^2 + 8/10^3 + 3/10^4 + 6/10^5 + 8/10^6 + ...

Solution

The series in the image is as follows:

1+310+6102+8103+3104+6105+8106+1 + \frac{3}{10} + \frac{6}{10^2} + \frac{8}{10^3} + \frac{3}{10^4} + \frac{6}{10^5} + \frac{8}{10^6} + \dots

This is a repeating decimal series. To find the sum, we can rewrite it as:

S=1+0.3+0.06+0.008+0.0003+0.00006+0.000008+S = 1 + 0.3 + 0.06 + 0.008 + 0.0003 + 0.00006 + 0.000008 + \dots

The series alternates in groups of terms with a specific repeating pattern: 3,6,83, 6, 8.

Step 1: Break the series into groups

The series can be written as:

S=1+(0.3+0.06+0.008)+(0.0003+0.00006+0.000008)+S = 1 + \left(0.3 + 0.06 + 0.008\right) + \left(0.0003 + 0.00006 + 0.000008\right) + \dots

Each group consists of three terms. Factoring this repeating structure can simplify the calculation.

Step 2: Write the repeating part as a geometric series

Within each group, the terms form a geometric series. For the first group:

G1=0.3+0.06+0.008G_1 = 0.3 + 0.06 + 0.008

For the second group:

G2=0.0003+0.00006+0.000008G_2 = 0.0003 + 0.00006 + 0.000008

The series progresses in powers of 10310^{-3}. Thus, the sum of the infinite series can be written as:

S=1+(0.3+0.06+0.008)(1+1103+1106+)S = 1 + \left(0.3 + 0.06 + 0.008\right) \cdot \left(1 + \frac{1}{10^3} + \frac{1}{10^6} + \dots\right)

Step 3: Simplify each geometric sum

The sum of the first group is:

0.3+0.06+0.008=0.3680.3 + 0.06 + 0.008 = 0.368

The factor 1+1103+1106+1 + \frac{1}{10^3} + \frac{1}{10^6} + \dots is an infinite geometric series with ratio 1103\frac{1}{10^3}. Its sum is:

Sum of the infinite geometric series=111103=110.001=10.9991.001\text{Sum of the infinite geometric series} = \frac{1}{1 - \frac{1}{10^3}} = \frac{1}{1 - 0.001} = \frac{1}{0.999} \approx 1.001

Step 4: Combine everything

The total sum of the series is:

S=1+0.3681.001S = 1 + 0.368 \cdot 1.001

Simplify further:

S1+0.3681.0011+0.368=1.368S \approx 1 + 0.368 \cdot 1.001 \approx 1 + 0.368 = 1.368

Final Answer:

1.368\boxed{1.368}

Would you like a detailed breakdown of any step or additional explanations?


Related Questions:

  1. What is the general formula for a geometric series and how is it applied?
  2. How does the repeating decimal pattern affect the convergence of the series?
  3. What are other methods to approach infinite series with repeating patterns?
  4. Can this series be converted into a fraction for an exact representation?
  5. How do small perturbations (like ±0.001\pm 0.001) impact calculations in such series?

Tip:

Understanding the geometric series formula is essential for working with infinite repeating patterns in mathematics.

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Math Problem Analysis

Mathematical Concepts

Infinite Series
Geometric Series
Decimal Expansion

Formulas

Sum of infinite geometric series: S = a / (1 - r)
Decimal notation as fractional values

Theorems

Convergence of geometric series
Properties of repeating decimals

Suitable Grade Level

Grades 9-12