Trong các sự kiện sau, sự kiện nào là sự kiện chắc chắn xảy ra?

1) a) \(8,712 \cdot 5,18 + 5,18 \cdot 2,788 + 11,5 \cdot 4,82\)

\[ = 5,18 \cdot \left( {8,712 + 2,788} \right) + 11,5 \cdot 4,82\]

\[ = 5,18 \cdot 11,5 + 11,5 \cdot 4,82\]

\[ = 11,5 \cdot \left( {5,18 + 4,82} \right)\]

\[ = 11,5 \cdot 10\]

\( = 115.\)

b) \(1,25:\frac{{15}}{{20}} + \left( {25\% - \frac{5}{6}} \right):4\frac{2}{3}\)

\( = \frac{{125}}{{100}}:\frac{3}{4} + \left( {\frac{{25}}{{100}} - \frac{5}{6}} \right):\frac{{14}}{3}\)

\( = \frac{6}{5} \cdot \frac{4}{3} + \left( {\frac{1}{4} - \frac{5}{6}} \right) \cdot \frac{3}{{14}}\)

\( = \frac{8}{5} + \left( {\frac{3}{{12}} - \frac{{10}}{{12}}} \right) \cdot \frac{3}{{14}}\)

\( = \frac{8}{5} + \frac{{ - 7}}{{12}} \cdot \frac{3}{{14}}\)

\( = \frac{8}{5} + \frac{{ - 1}}{8} = \frac{{64}}{{40}} - \frac{5}{{40}} = \frac{{59}}{{40}}\).