Answer :

[tex]Our \ GCF \ is \ 4 \\ \\ \frac{4:4}{20:4}= \frac{1}{5} \\ \\ \frac{4}{20} \ simplified \ is \ \frac{1}{5} \\ [/tex]
0000000
[tex]\sf \frac{4}{20}~\underrightarrow{\sf ~simplify~by~4~~}~\frac{4:4}{20:4} =\boxed{\sf \frac{1}{5} }[/tex]