How many 3-digit numbers have a first digit which is triple the final digit?
There are only three possibilities for the first digit: \[
\begin{array}{|c|c|}\hline
\text{First digit} & \text{Last digit} \\ \hline
3 & 1 \\ \hline
6 & 2 \\ \hline
9 & 3 \\ \hline
\end{array}
\] The middle digit can be any of the $10$ digits. The answer is $3\times 10=\boxed{30}.$