\[\boxed{\text{379\ (379).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \sqrt{\frac{2}{7}} = \frac{\sqrt{2}}{\sqrt{7}}\]
\[\textbf{б)}\ \sqrt{\frac{3}{10}} = \frac{\sqrt{3}}{\sqrt{10}}\]
\[\textbf{в)}\ \sqrt{\frac{5}{a}} = \frac{\sqrt{5}}{\sqrt{a}}\]
\[\textbf{г)}\ \sqrt{\frac{b}{3}} = \frac{\sqrt{b}}{\sqrt{3}}\]