\[\boxed{\text{7.8.}}\]
\[\textbf{а)}\ \frac{1}{25} = 1\ :25 = 0,04\]
\[\textbf{б)}\ \frac{1}{20} = 1\ :20 = 0,05\]
\[\textbf{в)}\ \frac{4}{5} = 4\ :5 = 0,8\]
\[\textbf{г)}\ \frac{1}{4} = 1\ :4 = 0,25\]
\[\textbf{д)}\ \frac{19}{10} = 19\ :10 = 1,9\]