Answer
$0.004$
Work Step by Step
Using the laws of exponents, the given expression, $
\dfrac{16\times10^5}{4\times10^8}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\dfrac{16}{4}\times10^{5-8}
\\\\=
4\times10^{-3}
.\end{array}
Since the exponent of $10$ is $\text{negative }
3
,$ move the decimal point $
3
$ places to the $\text{left.}$ Hence, the standard form of the expression above is
\begin{array}{l}\require{cancel}
0.004
.\end{array}