First, set up the equation for exponential decay: f(t) = P0e-rt, where P0 is the original amount of Carbon 14. To find the half life, we set the equation to half the original and t=5730.
P0 / 2 = P0e-5730r
r = (ln2)/5730
Now that we know what r is, we can simply solve for the time where f(t) = 0.897P0.
0.897 = e-rt.
t = -ln(0.897)/r ≈ 898.6
Thus, the mummy is approximately 899 years old.