\({\text{0}}{\text{.7 = }}\,\frac{{0.4x + 0.9y}}{{x + y}}\)
\( \Rightarrow \,{\text{0}}{\text{.7x + 0}}{\text{.7y = 0}}{\text{.4x + 0}}{\text{.9y}}\)
\( \Rightarrow \,\,{\text{0}}{\text{.3x = 0}}{\text{.2y}}\)
\( \Rightarrow \,\,\frac{x}{y}\,\, = \,\,\frac{{0.2}}{{0.3}}\, \Rightarrow \,\,\frac{x}{y}\,\, = \,\,\frac{2}{3}\)