3. A sum of $a$ rubles was deposited in a savings bank at the beginning of the year. After one year, this amount increased by $2 \%$. The newly obtained amount increased again by $2 \%$ after another year, and so on. How many rubles will be received after $n$ years? $(n \in N)$
3. S o l u t i o n. After one year, $102\% = 1.02$ of the invested amount will be received, i.e., $1.02a$ rubles. This amount will increase by two percent after another year, and the deposit will amount to $1.02 \cdot 1.02a = 1.02^2a$ rubles. After $n$ years, $1.02^n a$ rubles will be received.