Answer
$S=5$
Work Step by Step
$\displaystyle \sum_{n=0}^{∞}4(0.2)^n=4(0.2)^0+4(0.2)^1+4(0.2)^2+...$
$a_1=4(0.2)^0=4$
$r=\frac{a_2}{a_1}=\frac{4(0.2)^1}{4(0.2)^0}=0.2$
$S=\frac{a_1}{1-r}=\frac{4}{1-0.2}=\frac{4}{0.8}=5$
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