\[\boxed{\mathbf{3.16}}\]
\[\textbf{а)}\ 45\ :(30 + 25) = \frac{45}{55} =\]
\[= \frac{9}{11} \approx 0,8\%\]
\[\textbf{б)}\ 30\ :(45 + 25) = \frac{30}{70} =\]
\[= \frac{3}{7} \approx 0,4\%\]
\[\textbf{в)}\ 45\ :25 = \frac{45}{25} = \frac{9}{5} = 1,8\%\]
\[\textbf{г)}\ 30\ :45 = \frac{30}{45} = \frac{2}{3} \approx 0,7\%\]
\[\textbf{д)}\ 25\ :30 = \frac{25}{30} = \frac{5}{6} \approx 0,8\%\]