\(\sqrt{\dfrac{4}{9}}:\sqrt{\dfrac{25}{36}}\)
\(=\dfrac{\sqrt{4}}{\sqrt{9}}:\dfrac{\sqrt{25}}{\sqrt{36}}\)
\(=\dfrac{\sqrt{2^2}}{\sqrt{3^2}}:\dfrac{\sqrt{5^2}}{\sqrt{6^2}}\)
\(=\dfrac{2}{3}:\dfrac{5}{6}\)
\(=\dfrac{2}{3}\cdot\dfrac{6}{5}\)
\(=\dfrac{4}{5}\)