82 − 54
45 + 29
90 − 44
18 + 18
82 − 54 = (70 + 12) − (50 + 4) = (70 − 50) + (12 − 4) = 20 + 8 = 28
45 + 29 = (40 + 20) + (5 + 9) = 60 + 14 = 74
90 − 44 = (80 + 10) − (40 + 4) = (80 − 40) + (10 − 4) = 40 + 6 = 46
18 + 18 = (10 + 10) + (8 + 8) = 20 + 16 = 36