We can approach this problem without setting up an exponential equation. Here's a simple table, which we make with mental math.
$$ \begin{array} {|c|c|} \hline
\text{ population} & \text{time (minutes)} \\ \hline
1 & 0 \\ \hline
3 & 40 \\ \hline
9 & 80 \\ \hline
27 & 120 \\ \hline
\end{array}
$$
At 120 minutes (2 hours), the population is \(\boxed{27}\).
We can create a simple exponential equation:
$$ P = 1\cdot 3^t $$
Since we want for the population to triple every 40 minutes,
$$ P=1\cdot 3^{\frac{t}{40}} $$
There are 120 minutes in 2 hours:
$$ P = 1\cdot 3^{\frac{120}{40}} $$
$$ P=3^{3} $$
$$ P=\boxed{27} $$