A protein has three identical sites arranged at the vertices of an equilateral triangle. If one site is filled with a dye (donor), the measured quantum yield $\left(\phi_{D}\right)$ is $0.5$. Filling one site with a donor dye and a second site with an acceptor dye results in $\phi_{D}$ of $0.25$. The measured $\phi_{D}$ of one site filled with donor and the other two sites filled with acceptor dye (rounded off to three decimal places) is _____________.
