daca impartim un nr a la 5 apoi ii adaugam 16 obtinem acelasi nr a.sa se afle a

Răspuns :

a : 5+16 = a | ×5
a +16×5 = 5×a
5×a - a = 80
4×a = 80
a = 80:4
a = 20

Verificare:
20:5+16 = 4+16 = 20