Answer
$
N=10(1.13)^t
$
The population was growing by about $13 \%$ per year.
Work Step by Step
We know that $N=10$ when $t=0$, we want $N=10 b^t$ . Since $N=20000$ when $t=62$, we have
$$
\begin{aligned}
N & =10 b^t \\
20000 & =10 b^{62} \\
b^{62} & =\frac{20000}{10}=2000 \\
b & =(2000)^{1 / 62}=1.13 .
\end{aligned}
$$ Hence, $$
N=10(1.13)^t
$$ The population was growing by about $13 \%$ per year.
