8. Найдите все натуральные числа от 1 до 700, которые не делятся на 5. Сколько таких чисел? Обоснуйте ответ.

Числа, делящиеся на 5, заканчиваются цифрой 0 или 5. От 1 до 700 всего 700 натуральных чисел.

Количество чисел, делящихся на 5: \(700:5=140\).

Тогда количество чисел, которые не делятся на 5: \(700-140=560\).

Все такие числа:

1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 14, 16, 17, 18, 19, 21, 22, 23, 24, 26, 27, 28, 29, 31, 32, 33, 34, 36, 37, 38, 39, 41, 42, 43, 44, 46, 47, 48, 49, 51, 52, 53, 54, 56, 57, 58, 59, 61, 62, 63, 64, 66, 67, 68, 69, 71, 72, 73, 74, 76, 77, 78, 79, 81, 82, 83, 84, 86, 87, 88, 89, 91, 92, 93, 94, 96, 97, 98, 99, 101, 102, 103, 104, 106, 107, 108, 109, 111, 112, 113, 114, 116, 117, 118, 119, 121, 122, 123, 124, 126, 127, 128, 129, 131, 132, 133, 134, 136, 137, 138, 139, 141, 142, 143, 144, 146, 147, 148, 149, 151, 152, 153, 154, 156, 157, 158, 159, 161, 162, 163, 164, 166, 167, 168, 169, 171, 172, 173, 174, 176, 177, 178, 179, 181, 182, 183, 184, 186, 187, 188, 189, 191, 192, 193, 194, 196, 197, 198, 199, 201, 202, 203, 204, 206, 207, 208, 209, 211, 212, 213, 214, 216, 217, 218, 219, 221, 222, 223, 224, 226, 227, 228, 229, 231, 232, 233, 234, 236, 237, 238, 239, 241, 242, 243, 244, 246, 247, 248, 249, 251, 252, 253, 254, 256, 257, 258, 259, 261, 262, 263, 264, 266, 267, 268, 269, 271, 272, 273, 274, 276, 277, 278, 279, 281, 282, 283, 284, 286, 287, 288, 289, 291, 292, 293, 294, 296, 297, 298, 299, 301, 302, 303, 304, 306, 307, 308, 309, 311, 312, 313, 314, 316, 317, 318, 319, 321, 322, 323, 324, 326, 327, 328, 329, 331, 332, 333, 334, 336, 337, 338, 339, 341, 342, 343, 344, 346, 347, 348, 349, 351, 352, 353, 354, 356, 357, 358, 359, 361, 362, 363, 364, 366, 367, 368, 369, 371, 372, 373, 374, 376, 377, 378, 379, 381, 382, 383, 384, 386, 387, 388, 389, 391, 392, 393, 394, 396, 397, 398, 399, 401, 402, 403, 404, 406, 407, 408, 409, 411, 412, 413, 414, 416, 417, 418, 419, 421, 422, 423, 424, 426, 427, 428, 429, 431, 432, 433, 434, 436, 437, 438, 439, 441, 442, 443, 444, 446, 447, 448, 449, 451, 452, 453, 454, 456, 457, 458, 459, 461, 462, 463, 464, 466, 467, 468, 469, 471, 472, 473, 474, 476, 477, 478, 479, 481, 482, 483, 484, 486, 487, 488, 489, 491, 492, 493, 494, 496, 497, 498, 499, 501, 502, 503, 504, 506, 507, 508, 509, 511, 512, 513, 514, 516, 517, 518, 519, 521, 522, 523, 524, 526, 527, 528, 529, 531, 532, 533, 534, 536, 537, 538, 539, 541, 542, 543, 544, 546, 547, 548, 549, 551, 552, 553, 554, 556, 557, 558, 559, 561, 562, 563, 564, 566, 567, 568, 569, 571, 572, 573, 574, 576, 577, 578, 579, 581, 582, 583, 584, 586, 587, 588, 589, 591, 592, 593, 594, 596, 597, 598, 599, 601, 602, 603, 604, 606, 607, 608, 609, 611, 612, 613, 614, 616, 617, 618, 619, 621, 622, 623, 624, 626, 627, 628, 629, 631, 632, 633, 634, 636, 637, 638, 639, 641, 642, 643, 644, 646, 647, 648, 649, 651, 652, 653, 654, 656, 657, 658, 659, 661, 662, 663, 664, 666, 667, 668, 669, 671, 672, 673, 674, 676, 677, 678, 679, 681, 682, 683, 684, 686, 687, 688, 689, 691, 692, 693, 694, 696, 697, 698, 699.

Ответ: 560 чисел.