34 + 18 O 35 + 18;
63 + 20 O 62 + 20;
17 + 9 O 18 + 8;
13 − 7 O 13 − 8.
34 + 18 < 35 + 18
34 + 18 = (30 + 4) + (10 + 8) = (30 + 10) + (8 + 4) = 40 + 12 = 40 + 10 + 2 = 50 + 2 = 52;
35 + 18 = (30 + 5) + (10 + 8) = (30 + 10) + (8 + 5) = 40 + 13 = 40 + 10 + 3 = 50 + 3 = 53;
52 < 53
63 + 20 > 62 + 20
63 + 20 = (60 + 3) + 20 = (60 + 20) + 3 = 80 + 3 = 83;
62 + 20 = (60 + 2) + 20 = (60 + 20) + 2 = 80 + 2 = 82;
83 > 82
17 + 9 = 18 + 8
17 + 9 = 17 + 3 + 6 = 20 + 6 = 26;
18 + 8 = 18 + 2 + 6 = 20 + 6 = 26;
26 = 26
13 − 7 > 13 − 8
13 − 7 = 13 − 3 − 4 = 10 − 4 = 6;
13 − 8 = 13 − 3 − 5 = 10 − 5 = 5;
6 > 5
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