Ответ:

  1. 57 − 7 + 40 = 50 + 40 = 90;
  2. 45 − (26 + 8) = 45 − 34 = 11;
  3. 41 + 9 − 25 = 50 − 25 = 25;
  4. 2 · 1 + 0 = 2 + 0 = 2.