Answer
$S_5=24.96$
Work Step by Step
$\displaystyle \sum_{i=1}^{4}20(0.2)^{i-1}=20(0.2)^0+20(0.2)^1+20(0.2)^2+20(0.2)^3$
$a_1=20(0.2)^0=20$
$r=\frac{a_2}{a_1}=\frac{20(0.2)^1}{20(0.2)^0}=0.2$
$S_5=a_1(\frac{1-r^n}{1-r})=20(\frac{1-0.2^4}{1-0.2})=20~\frac{0.9984}{0.8}=24.96$
