[tex]\overline{1ab} \; \vdots \; 5 \Leftrightarrow b\in\lbrace0,5\rbrace\\
\overline{1ab} \; \vdots \; 4 \Leftrightarrow \overline{ab}\in M_4\\
\overline{1a0} \; \vdots \; 4 \Rightarrow a\in\lbrace0,2,4,6,8\rbrace\\
\overline{1a5} \; \vdots \; 4 \Rightarrow a\in \oslash\\
Asadar, \; \overline{1ab} \; \vdots \; 20 \in \lbrace{100,120,140,160,180}\rbrace[/tex]
