Answer:
240 teachers
Step-by-step explanation:
Let u be 1 unit.
1u+12u=260
13u=260
u=260÷13
=20
No. of teachers=12u=20×12
=240
Let teacher be x
[tex]\\ \sf\longmapsto x+12x=260[/tex]
[tex]\\ \sf\longmapsto 13x=260[/tex]
[tex]\\ \sf\longmapsto x=\dfrac{260}{13}[/tex]
[tex]\\ \sf\longmapsto x=20[/tex]