15 + 18 + 2;
45 + 5 + 26;
37 + 19 + 3;
56 + 20;
50 + 26;
56 + 6;
60 − 32;
80 − 32;
50 − 32.
15 + 18 + 2 = 15 + (18 + 2) = 15 + 20 = 35
45 + 5 + 26 = 50 + 26 = 76
37 + 19 + 3 = (37 + 3) + 19 = 40 + 19 = 59
56 + 20 = (50 + 6) + 20 = (50 + 20) + 6 = 70 + 6 = 76
50 + 26 = 50 + (20 + 6) = (50 + 20) + 6 = 70 + 6 = 76
56 + 6 = 50 + (6 + 6) = 50 + 12 = 62
60 − 32 = 60 − 30 − 2 = 30 − 2 = 28
80 − 32 = 80 − 30 − 2 = 50 − 2 = 48
50 − 32 = 50 − 30 − 2 = 20 − 2 = 18
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