\[\boxed{\mathbf{319.}}\]
\[Набор\ должен\ состоять\ \]
\[из\ одинаковых\ чисел:\]
\[5,\ 5,\ 5,\ 5,\ 5,\ 5,\ 5,\ 5,\ 5,\ 5.\]
\[\overline{x} = \frac{50}{10} = 5;\]
\[\overline{x^{2}} = \frac{25 \cdot 10}{10} = 25;\]
\[S^{2} = \overline{x^{2}} - {\overline{x}}^{2} = 25 - 5^{2} =\]
\[= 25 - 25 = 0.\]
\[S = \sqrt{0} = 0.\]