13.219. The population of the city increases annually by $1 / 50$ of the current number of residents. In how many years will the population triple?
Solution.

Using the compound interest formula $x\left(\frac{1}{50}+1\right)^{n}=3 x$, we find $n=\log _{3} 1.02 \approx 55$.

Answer: $\approx 55$ years.