Total cards signed:-
[tex]\\ \tt\longmapsto \dfrac{1}{4}+\dfrac{3}{5}[/tex]
[tex]\\ \tt\longmapsto \dfrac{5+12}{20}=\dfrac{17}{20}[/tex]
Cards left:-
[tex]\\ \tt\longmapsto 80-17/20(80)=80-68=12[/tex]
