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Find the sum of the first 6 terms of the following series, to the nearest integer.

20,10,5,dots
Answer:

Find the sum of the first 66 terms of the following series, to the nearest integer.\newline20,10,5, 20,10,5, \ldots \newlineAnswer:

Full solution

Q. Find the sum of the first 66 terms of the following series, to the nearest integer.\newline20,10,5, 20,10,5, \ldots \newlineAnswer:
  1. Identify type and ratio: Identify the type of series and the common ratio.\newlineThe given series is geometric because each term is obtained by multiplying the previous term by a constant ratio.\newlineTo find the common ratio rr, we divide the second term by the first term.\newliner=1020=0.5r = \frac{10}{20} = 0.5
  2. Use formula for sum: Use the formula for the sum of the first nn terms of a geometric series.\newlineThe sum SnS_n of the first nn terms of a geometric series is given by the formula:\newlineSn=a×(1rn)/(1r)S_n = a \times (1 - r^n) / (1 - r), where aa is the first term, rr is the common ratio, and nn is the number of terms.\newlineIn this case, a=20a = 20, r=0.5r = 0.5, and n=6n = 6.
  3. Calculate sum of terms: Calculate the sum of the first 66 terms.\newlineS6=20×(10.56)/(10.5)S_6 = 20 \times (1 - 0.5^6) / (1 - 0.5)\newlineS6=20×(10.015625)/0.5S_6 = 20 \times (1 - 0.015625) / 0.5\newlineS6=20×0.984375/0.5S_6 = 20 \times 0.984375 / 0.5\newlineS6=19.6875/0.5S_6 = 19.6875 / 0.5\newlineS6=39.375S_6 = 39.375\newlineSince we need to round to the nearest integer, the sum is approximately 3939.

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