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Find the value of the following expression and round to the nearest integer:

sum_(n=2)^(57)20(1.15)^(n-2)
Answer:

Find the value of the following expression and round to the nearest integer:\newlinen=25720(1.15)n2 \sum_{n=2}^{57} 20(1.15)^{n-2} \newlineAnswer:

Full solution

Q. Find the value of the following expression and round to the nearest integer:\newlinen=25720(1.15)n2 \sum_{n=2}^{57} 20(1.15)^{n-2} \newlineAnswer:
  1. Given geometric series: We are given a geometric series with the first term a=20(1.15)22=20a = 20(1.15)^{2-2} = 20 and a common ratio r=1.15r = 1.15. The sum of a finite geometric series can be found using the formula Sn=a(1rn)1rS_n = \frac{a(1 - r^n)}{1 - r}, where nn is the number of terms.
  2. Determine number of terms: First, we need to determine the number of terms in the series. Since the series starts at n=2n=2 and goes to n=57n=57, the number of terms is 572+1=5657 - 2 + 1 = 56.
  3. Apply sum formula: Now we can apply the formula for the sum of a geometric series: Sn=a(1rn)/(1r)S_n = a(1 - r^n) / (1 - r). Plugging in the values, we get S56=20(11.1556)/(11.15)S_{56} = 20(1 - 1.15^{56}) / (1 - 1.15).
  4. Calculate numerator: Let's calculate the numerator of the fraction: 11.15561 - 1.15^{56}. Using a calculator, we find that 1.1556142.0611.15^{56} \approx 142.061.
  5. Calculate denominator: Subtracting this from 11 gives us 1142.061141.0611 - 142.061 \approx -141.061.
  6. Divide numerator by denominator: Now we calculate the denominator of the fraction: 11.15=0.151 - 1.15 = -0.15.
  7. Multiply by first term: We can now divide the numerator by the denominator: 141.061/0.15940.407-141.061 / -0.15 \approx 940.407.
  8. Round to nearest integer: Multiplying this result by the first term of the series 2020 gives us the sum of the series: 940.407×2018808.14940.407 \times 20 \approx 18808.14.
  9. Round to nearest integer: Multiplying this result by the first term of the series 2020 gives us the sum of the series: 940.407×2018808.14940.407 \times 20 \approx 18808.14.Finally, we round the result to the nearest integer: 18808.1418808.14 rounds to 1880818808.

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