H-elevii care practica numai handbal
V-elevii care practica numai volei
C-elevii care practica ambele sporturi
H+V+C=25
H+C=17
V+C=14
adunand ultimele doua relatii:H+V+C+C=31⇔25+C=31⇔C=31-25⇔C=6 ambele sporturi
H=17-6=11 numai handbal
V=14-6=8 numai volei
Verificare: 11+8+6=25 elevi