2 мин = 120 с
9 мин = 540 с
6 мин 20 с = 380 с
7 мин 12 с = 432 с
5 мин 2 с = 302 с
Вычисления:
2 мин = 60 * 2 = (6 * 2) * 10 = 12 * 10 = 120 с
9 мин = 60 * 9 = (6 * 9) * 10 = 54 * 10 = 540 с
6 мин 20 с = 60 * 6 + 20 = (6 * 6) * 10 + 20 = 36 * 10 + 20 = 360 + 20 = 380 с
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}360\\ 20\end{array}}\\ \begin{array}{r}380\end{array}\end{array}$
7 мин 12 с = 60 * 7 + 12 = (6 * 7) * 10 + 12 = 42 * 10 + 12 = 420 + 12 = 432 с
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}420\\ 12\end{array}}\\ \begin{array}{r}432\end{array}\end{array}$
5 мин 2 с = 60 * 5 + 2 = (6 * 5) * 10 + 2 = 30 * 10 + 2 = 300 + 2 = 302 с
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}300\\ 2\end{array}}\\ \begin{array}{r}302\end{array}\end{array}$