Номер 25

37 + 9 = (37 + 3) + 6 = 40 + 6 = 46;
37 + 9 = 30 + (7 + 9) = 30 + 16 = 46;
26 + 17 = (26 + 10) + 7 = 36 + 7 = 43;
26 + 17 = (20 + 10) + (6 + 7) = 30 + 13 = 43;
37 – 9 = (37 – 7) – 2 = 30 – 2 = 28;
37 – 9 = 20 + (17 – 9) = 20 + 8 = 28;
42 – 26 = (42 – 20) – 6 = 22 – 6 = 16;
42 – 26 = (42 – 2) – 24 = 40 – 24 = 16.

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