Answer
${\large Q=10,000e^{-0.139t} }$
Work Step by Step
This is an exponential decay problem with,
$\quad Q=Q_{0}e^{-kt}$
where, $Q_{0}=10,000$
From the half-life formula, we have:
$ \left\{\begin{array}{ll}
t_{h}k & =\ln 2\\
5k & =\ln 2\\
k & =\frac{\ln 2}{5}\approx 0.139
\end{array}\right.$
We plug in the $Q_o$ and $k$ values:
$Q=Q_{0}e^{-kt}$
${\large Q=10,000e^{-0.139t} }$
