'Maths Tuition' and 'Secretary cum Administrator' is correct English.

'Tuition' is the verb of the noun 'tutor' eg.

In an advert offering tutoring services one would write "....Maths tuition also offered" ie the tutor can also teach(verb) Maths.
If one wrote ".....Maths tutor also offered" - this would mean that ANOTHER person(noun) would be teaching the Maths aspect of the education.