\[\boxed{\mathbf{251.}}\]
\[x - вероятность\ каждого\ \]
\[элементарного\ события.\]
\[\textbf{а)}\ 25x = 1\]
\[x = \frac{1}{25}\]
\[x = 0,04.\]
\[\textbf{б)}\ 17x = 1\]
\[x = \frac{1}{17}.\]
\[\textbf{в)}\ 100x = 1\]
\[x = \frac{1}{100}\]
\[x = 0,01.\]