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Write the repeating decimal as a fraction.\newline.81818181.81818181

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Q. Write the repeating decimal as a fraction.\newline.81818181.81818181
  1. Rephrase Problem: Let's first rephrase the problem into a single "How can we express the repeating decimal 0.818181810.81818181\ldots as a fraction?"
  2. Identify Repeating Pattern: Identify the repeating pattern in the decimal. The digits "8181" repeat indefinitely, so we can write the decimal as 0.81818181=0.81+0.0081+0.000081+0.81818181\ldots = 0.81 + 0.0081 + 0.000081 + \ldots
  3. Express Terms as Fractions: Express each term in the pattern as a fraction. The first term is 0.810.81, which is 81100\frac{81}{100}. The second term is 0.00810.0081, which is 8110000\frac{81}{10000}, and so on. This gives us the series: 81100+8110000+811000000+\frac{81}{100} + \frac{81}{10000} + \frac{81}{1000000} + \ldots
  4. Recognize Geometric Series: Recognize that the series forms a geometric series, where each term is 1100\frac{1}{100} times the previous term. The first term (a1)(a_1) is 81100\frac{81}{100}, and the common ratio (r)(r) is 1100\frac{1}{100}.
  5. Use Sum Formula: Use the formula for the sum of an infinite geometric series, which is a1/(1r)a_1 / (1 - r), where a1a_1 is the first term and rr is the common ratio. Substitute a1=81100a_1 = \frac{81}{100} and r=1100r = \frac{1}{100} into the formula.
  6. Calculate Sum: Calculate the sum of the series: (81100)/(11100)=(81100)/(99100)=81100×10099=8199(\frac{81}{100}) / (1 - \frac{1}{100}) = (\frac{81}{100}) / (\frac{99}{100}) = \frac{81}{100} \times \frac{100}{99} = \frac{81}{99}.
  7. Simplify Fraction: Simplify the fraction 8199\frac{81}{99}. Both the numerator and the denominator are divisible by 99. Dividing both by 99 gives us 911\frac{9}{11}.

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