Ответ:\(30\ 999 + 1 = 31\ 000\).\(10\ 000 - 1 = 9\ 999\).\(25\ 909 + 1 = 25\ 910\).\(100\ 000 - 1 = 99\ 999\).\(90\ 100 - 1 = 90\ 099\).\(40\ 000 - 1 = 39\ 999\).\(39\ 099 + 1 = 39\ 100\).\(699\ 999 + 1 = 700\ 000\).