Answer
54.62 %
Work Step by Step
The half-life for carbon is 5730 years.
so, $k=\dfrac{\ln 2}{5730}$
$C=C_0e^{-\dfrac{\ln 2}{5730}t}$
Now, at $t=5000$
$C=C_0e^{-\dfrac{\ln 2}{5730}(5000)}$
so, $C \approx 0.5462 C_0$
This means that 54.62 % of carbon-14 remained in Otzi at the time of discovery in 1991.
