Ответ:

  1. (374 + 978) + 626 = (374 + 626) + 978 = 1 000 + 978 = 1 978.
  2. 787 + 476 + 524 = 787 + (476 + 524) = 787 + 1 000 = 1 787.
  3. 242 + 537 + 358 + 263 = (242 + 358) + (537 + 263) = 600 + 800 = 1 400.
  4. (1 685 + 14 703) + (5 297 + 2 315) = (1 685 + 2 315) + (14 703 + 5 297) = 4 000 + 20 000 = 24 000.