Answer
57 minutes
Work Step by Step
The first case started with one amoeba, the number of amoeba after t minutes is $N=2^{t/3}$
Let $t=1hour=60minites$, we have $N=2^{20}$.
For the second case, we start with two amoebas, the number of amoebas after t minutes is
$N1=2^{t/3}+2^{t/3}=2^{t/3+1}$. Set $N1=N$, we have
$t/3+1=20$ and $t=19\times3=57minutes$
