Условие:

70 − 5
80 − 4
100 − 4
100 − 9
52 + 8
60 − 8
43 − 20
43 − 2

70 − 5 = (60 + 10) − 5 = 60 + (10 − 5) = 60 + 5 = 65
80 − 4 = (70 + 10) − 4 = 70 + (10 − 4) = 70 + 6 = 76
100 − 4 = (90 + 10) − 4 = 90 + (10 − 4) = 90 + 6 = 96
100 − 9 = (90 + 10) − 9 = 90 + (10 − 6) = 90 + 1 = 91
52 + 8 = (50 + 2) + 8 = 50 + (2 + 8) = 50 + 10 = 60
60 − 8 = (50 + 10) − 8 = 50 + (10 − 8) = 50 + 2 = 52
43 − 20 = (40 + 3) − 20 = 3 + (40 − 20) = 3 + 20 = 23
43 − 2 = (40 + 3) − 2 = 40 + (3 − 2) = 40 + 1 = 41