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Find the sum of the first 7 terms of the following series, to the nearest integer.

25,100,400,dots
Answer:

Find the sum of the first 77 terms of the following series, to the nearest integer.\newline25,100,400, 25,100,400, \ldots \newlineAnswer:

Full solution

Q. Find the sum of the first 77 terms of the following series, to the nearest integer.\newline25,100,400, 25,100,400, \ldots \newlineAnswer:
  1. Identify type and ratio: Identify the type of series and the common ratio.\newlineThe given series is geometric because each term after the first is obtained by multiplying the previous term by a constant number.\newlineTo find the common ratio rr, we divide the second term by the first term.\newline10025=4\frac{100}{25} = 4\newlineCommon Ratio: 44
  2. Use sum formula: Use the formula for the sum of the first nn terms of a geometric series.\newlineThe formula for the sum of the first nn terms (SnS_n) of a geometric series is:\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=25a = 25, r=4r = 4, and n=7n = 7.
  3. Substitute and calculate: Substitute the values into the formula and calculate the sum.\newlineS7=25×(147)/(14)S_7 = 25 \times (1 - 4^7) / (1 - 4)\newlineS7=25×(116384)/(14)S_7 = 25 \times (1 - 16384) / (1 - 4)\newlineS7=25×(16383)/(3)S_7 = 25 \times (-16383) / (-3)\newlineS7=25×5461S_7 = 25 \times 5461\newlineS7=136525S_7 = 136525
  4. Round to nearest integer: Round the sum to the nearest integer.\newlineThe sum of the first 77 terms is 136525136525, which is already an integer, so no rounding is necessary.

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