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Question 1
17421

The sum of the first eight terms of the G.P. \(5 + 15 + ....\) is?

\(16400\)

$$
\begin{aligned}
a=5 \quad  r&=\frac{15}{5}=3 \\
 S_{n}&=\frac{a\left(r^{n}-1\right)}{r-1}\\ \rightarrow S_{8}&=\frac{5\left(3^{8}-1\right)}{3-1}\\&=16400
\end{aligned}
$$

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