5) \(\left(\sqrt{2\dfrac25}-\sqrt{5\dfrac25}\right):\sqrt{\dfrac3{125}}\)

\[\sqrt{2\dfrac25}=\sqrt{\dfrac{12}5}=\dfrac{2\sqrt{15}}5,\qquad \sqrt{5\dfrac25}=\sqrt{\dfrac{27}5}=\dfrac{3\sqrt{15}}5.\]

\[\left(\dfrac{2\sqrt{15}}5-\dfrac{3\sqrt{15}}5\right):\sqrt{\dfrac3{125}}=-\dfrac{\sqrt{15}}5:\dfrac{\sqrt3}{5\sqrt5}=-5.\]

Ответ: −5