Решение:
1) (9 + 6) : 3 = 15 : 3 = 5
(20 – 2) : 3 = 18 : 3 = 6
(20 + 1) : 3 = 21 : 3 = 7
2) (50 – 20) : 3 = 30 : 3 = 10
40 : 10 * 3 = 4 * 3 = 12
50 : 5 * 3 = 10 * 3 = 30