Ответ:

  1. 73 + 26 = 73 + 20 + 6 = 93 + 6 = 99.

  2. 34 + 66 = 100.

  3. 87 − 38 = 87 − 30 − 8 = 57 − 8 = 49.

  4. 63 + 19 = 63 + 20 − 1 = 83 − 1 = 82.