Ответ:

  1. \(30\ 999 + 1 = 31\ 000\).
  2. \(10\ 000 - 1 = 9\ 999\).
  3. \(25\ 909 + 1 = 25\ 910\).
  4. \(100\ 000 - 1 = 99\ 999\).
  5. \(90\ 100 - 1 = 90\ 099\).
  6. \(40\ 000 - 1 = 39\ 999\).
  7. \(39\ 099 + 1 = 39\ 100\).
  8. \(699\ 999 + 1 = 700\ 000\).