Answer
$S=5$
Work Step by Step
$\displaystyle \sum_{n=0}^{∞}(0.8)^n=(0.8)^0+(0.8)^1+(0.8)^2+...$
$a_1=(0.8)^0=1$
$r=\frac{a_2}{a_1}=\frac{(0.8)^1}{(0.8)^0}=0.8$
$S=\frac{a_1}{1-r}=\frac{1}{1-0.8}=\frac{1}{0.2}=5$
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