Răspuns:
(50+20) : 10=70:10=7
sau
50:10+20:10=5+2=7
(40+50) : 10=90:10=9
40:10+50:10=9
(30+20) : 10=50:10=5
30:10+20:10=5
(60-40) : 10=20:10=2
60:10-40:10=2