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Find the sum of the first 50 terms in this geometric series:

1+(10)/(11)+(100)/(121)dots
Choose 1 answer:
(A) 0.01
(B) 0.99
(C) 10.91
(D) 11

Find the sum of the first 5050 terms in this geometric series:\newline1+1011+100121 1+\frac{10}{11}+\frac{100}{121} \ldots \newlineChoose 11 answer:\newline(A) 00.0101\newline(B) 00.9999\newline(C) 10.91 \mathbf{1 0 . 9 1} \newline(D) 1111

Full solution

Q. Find the sum of the first 5050 terms in this geometric series:\newline1+1011+100121 1+\frac{10}{11}+\frac{100}{121} \ldots \newlineChoose 11 answer:\newline(A) 00.0101\newline(B) 00.9999\newline(C) 10.91 \mathbf{1 0 . 9 1} \newline(D) 1111
  1. Identifying the series: We are given a geometric series:\newline1+1011+100121+1 + \frac{10}{11} + \frac{100}{121} + \ldots\newlineFirst, we need to identify the first term (aa) and the common ratio (rr) of the series.\newlineThe first term aa is clearly 11.\newlineTo find the common ratio rr, we divide the second term by the first term:\newliner=10111=1011r = \frac{\frac{10}{11}}{1} = \frac{10}{11}
  2. Finding the common ratio: Now that we have the first term a=1a = 1 and the common ratio r=1011r = \frac{10}{11}, we can use the formula for the sum of the first nn terms of a geometric series:\newlineSn=a(1rn)(1r)S_n = \frac{a(1 - r^n)}{(1 - r)}, where SnS_n is the sum of the first nn terms.\newlineWe want to find the sum of the first 5050 terms, so n=50n = 50.
  3. Using the formula for the sum: Let's plug the values into the formula:\newlineS50=1(1(1011)50)11011S_{50} = \frac{1(1 - (\frac{10}{11})^{50})}{1 - \frac{10}{11}}
  4. Plugging in the values: Simplify the denominator:\newline11011=11111011=1111 - \frac{10}{11} = \frac{11}{11} - \frac{10}{11} = \frac{1}{11}\newlineSo, S50=1(1(1011)50)111S_{50} = \frac{1(1 - (\frac{10}{11})^{50})}{\frac{1}{11}}
  5. Simplifying the denominator: Now, we multiply both the numerator and the denominator by 1111 to simplify the fraction:\newlineS50=11(1(1011)50)S_{50} = 11(1 - (\frac{10}{11})^{50})
  6. Multiplying by 1111: We can now calculate (1011)50(\frac{10}{11})^{50}, but since this is a very small number (because 1011\frac{10}{11} is less than 11 and we are raising it to the 50th50^{\text{th}} power), it will have a negligible effect on the sum. Therefore, we can approximate the sum by ignoring this term:\newlineS5011(10)S_{50} \approx 11(1 - 0)\newlineS5011S_{50} \approx 11
  7. Approximating the sum: The sum of the first 5050 terms in the given geometric series is approximately 1111.

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