$\text{a)}\frac{1}{4}=\frac{25}{100}=0,25$

$\text{b)}\frac{2}{5}=\frac{4}{10}=0,4$

$\text{c)}\frac{21}{50}=\frac{42}{100}=0,42$

$\text{d)}4\frac{17}{25}=4\frac{68}{100}=4,68$

$\text{e)}\frac{19}{8}=2\frac{3}{8}=2\frac{15}{40}=2\frac{75}{200}=2\frac{375}{1000}=2,375$

$\text{f)}\frac{73}{20}=3\frac{13}{20}=3\frac{65}{100}=3,65$

$\text{g)}\frac{77}{125}=\frac{77\cdot 8}{125\cdot 8}=\frac{616}{1000}=0,616$