Question

If the first term and common ratio is $5$, find the sum of first 8 terms of G.P.

• A. $188280$
• B. $288280$
• C. $388280$
• D. $488280$

Answer 1

Answer: (D)

$488280$

Given, first term $,a=5$, common ratio $,r=5$, $n=8$
We know $S_n=\frac{a_1(r^n-1)}{r-1}$
$S_8=\frac{5\left(\right(5{)}^8-1)}{\left(5\right)-1}$
$=\frac{5\left(\right(5{)}^8-1)}{4}$
$=488280$