We know that
Half-life is modeled by the formula
An=A0*(0.5)<span>^[t/h)]
where
An----------> </span>is the amount remaining after a time t
A0----------> is the initial quantity
t------------> is the time
h------------> is the half-life of the decaying quantity
in this problem
h=1601 years
A0=50 g
An=?
t=100 years
An=A0*(0.5)^[t/h)]---------> An=50*(0.5)^[100/1601)]-----> 47.88 gr
the answer is 47.88 g