60 − 5
40 − 7
30 + 28
52 − 30
33 + 7
80 − 5
58 + 2 − 4
78 + 20 − 6
60 − 5 = (50 + 10) − 5 = 50 + (10 − 5) = 50 + 5 = 55
40 − 7 = (30 + 10) − 7 = 30 + (10 − 7) = 30 + 3 = 33
30 + 28 = 30 + 20 + 8 = 50 + 8 = 58
52 − 30 = (50 + 2) − 30 = 2 + (50 − 30) = 2 + 20 = 22
33 + 7 = 30 + 3 + 7 = 30 + 10 = 40
80 − 5 = (70 + 10) − 5 = 70 + (10 − 5) = 70 + 5 = 75
58 + 2 − 4 = 60 − 4 = 56
78 + 20 − 6 = 98 − 6 = 92