用7、3、9这3个数字能摆出多少个不同的三位数?能详细说明具体的算法吗??

用7、3、9这3个数字能摆出多少个不同的三位数?能详细说明具体的算法吗??

3*2*1=6
第一位有三种，选定后，第二位有两种，选 定后最后一位只有一种

18种

397列举法 379，排十位2种,739,793,937,973 6个 利用乘法原理第一步 排百位3种

739,793 937,973 397,379 怎么算应该很明确了吧

6种！！！！ 每个数字开头都有2种， 有3个数字，3x2=6嘛~~ 笨耶~~

这里有个问题，就是数字的首位数可不可以是0？虽然说首位的0常常是省略掉的，但是写的话也不能算错，所以还是你自己来判断吧。结论是：如果首位不允许为0，那么共有60种，如果首位可以为0，那么共有228种。所有解都列在下面： 1 + 42 + 695 = 0738 1 + 43 + 685 = 0729 1 + 45 + 683 = 0729 1 + 45 + 692 = 0738 1 + 52 + 793 = 0846 1 + 53 + 792 = 0846 1 + 72 + 386 = 0459 1 + 72 + 395 = 0468 1 + 75 + 392 = 0468 1 + 76 + 382 = 0459 1 + 82 + 376 = 0459 1 + 82 + 493 = 0576 1 + 83 + 492 = 0576 1 + 83 + 645 = 0729 1 + 85 + 643 = 0729 1 + 86 + 372 = 0459 1 + 92 + 375 = 0468 1 + 92 + 483 = 0576 1 + 92 + 645 = 0738 1 + 92 + 753 = 0846 1 + 93 + 482 = 0576 1 + 93 + 752 = 0846 1 + 95 + 372 = 0468 1 + 95 + 642 = 0738 2 + 41 + 695 = 0738 2 + 45 + 691 = 0738 2 + 46 + 987 = 1035 2 + 47 + 986 = 1035 2 + 51 + 793 = 0846 2 + 53 + 764 = 0819 2 + 53 + 791 = 0846 2 + 54 + 763 = 0819 2 + 63 + 754 = 0819 2 + 64 + 753 = 0819 2 + 64 + 987 = 1053 2 + 67 + 984 = 1053 2 + 71 + 386 = 0459 2 + 71 + 395 = 0468 2 + 75 + 391 = 0468 2 + 76 + 381 = 0459 2 + 81 + 376 = 0459 2 + 81 + 493 = 0576 2 + 83 + 491 = 0576 2 + 84 + 967 = 1053 2 + 86 + 371 = 0459 2 + 86 + 947 = 1035 2 + 87 + 946 = 1035 2 + 87 + 964 = 1053 2 + 91 + 375 = 0468 2 + 91 + 483 = 0576 2 + 91 + 645 = 0738 2 + 91 + 753 = 0846 2 + 93 + 481 = 0576 2 + 93 + 751 = 0846 2 + 95 + 371 = 0468 2 + 95 + 641 = 0738 3 + 41 + 685 = 0729 3 + 45 + 681 = 0729 3 + 45 + 978 = 1026 3 + 48 + 975 = 1026 3 + 51 + 792 = 0846 3 + 52 + 764 = 0819 3 + 52 + 791 = 0846 3 + 54 + 762 = 0819 3 + 62 + 754 = 0819 3 + 64 + 752 = 0819 3 + 74 + 985 = 1062 3 + 75 + 948 = 1026 3 + 75 + 984 = 1062 3 + 78 + 945 = 1026 3 + 81 + 492 = 0576 3 + 81 + 645 = 0729 3 + 82 + 491 = 0576 3 + 84 + 975 = 1062 3 + 85 + 641 = 0729 3 + 85 + 974 = 1062 3 + 91 + 482 = 0576 3 + 91 + 752 = 0846 3 + 92 + 481 = 0576 3 + 92 + 751 = 0846 4 + 35 + 987 = 1026 4 + 37 + 985 = 1026 4 + 38 + 579 = 0621 4 + 39 + 578 = 0621 4 + 52 + 763 = 0819 4 + 53 + 762 = 0819 4 + 62 + 753 = 0819 4 + 62 + 987 = 1053 4 + 63 + 752 = 0819 4 + 67 + 982 = 1053 4 + 68 + 279 = 0351 4 + 69 + 278 = 0351 4 + 73 + 985 = 1062 4 + 75 + 983 = 1062 4 + 78 + 269 = 0351 4 + 78 + 539 = 0621 4 + 79 + 268 = 0351 4 + 79 + 538 = 0621 4 + 82 + 967 = 1053 4 + 83 + 975 = 1062 4 + 85 + 937 = 1026 4 + 85 + 973 = 1062 4 + 87 + 935 = 1026 4 + 87 + 962 = 1053 5 + 34 + 987 = 1026 5 + 37 + 984 = 1026 5 + 41 + 683 = 0729 5 + 41 + 692 = 0738 5 + 42 + 691 = 0738 5 + 43 + 681 = 0729 5 + 43 + 978 = 1026 5 + 48 + 973 = 1026 5 + 71 + 392 = 0468 5 + 72 + 391 = 0468 5 + 73 + 948 = 1026 5 + 73 + 984 = 1062 5 + 74 + 983 = 1062 5 + 78 + 943 = 1026 5 + 81 + 643 = 0729 5 + 83 + 641 = 0729 5 + 83 + 974 = 1062 5 + 84 + 937 = 1026 5 + 84 + 973 = 1062 5 + 87 + 934 = 1026 5 + 91 + 372 = 0468 5 + 91 + 642 = 0738 5 + 92 + 371 = 0468 5 + 92 + 641 = 0738 6 + 27 + 498 = 0531 6 + 28 + 479 = 0513 6 + 28 + 497 = 0531 6 + 29 + 478 = 0513 6 + 42 + 987 = 1035 6 + 47 + 298 = 0351 6 + 47 + 982 = 1035 6 + 48 + 297 = 0351 6 + 58 + 179 = 0243 6 + 59 + 178 = 0243 6 + 71 + 382 = 0459 6 + 72 + 381 = 0459 6 + 78 + 159 = 0243 6 + 78 + 429 = 0513 6 + 79 + 158 = 0243 6 + 79 + 428 = 0513 6 + 81 + 372 = 0459 6 + 82 + 371 = 0459 6 + 82 + 947 = 1035 6 + 87 + 942 = 1035 6 + 97 + 248 = 0351 6 + 97 + 428 = 0531 6 + 98 + 247 = 0351 6 + 98 + 427 = 0531 7 + 26 + 498 = 0531 7 + 28 + 496 = 0531 7 + 34 + 985 = 1026 7 + 35 + 984 = 1026 7 + 42 + 986 = 1035 7 + 46 + 298 = 0351 7 + 46 + 982 = 1035 7 + 48 + 296 = 0351 7 + 58 + 169 = 0234 7 + 59 + 168 = 0234 7 + 62 + 984 = 1053 7 + 64 + 982 = 1053 7 + 68 + 159 = 0234 7 + 69 + 158 = 0234 7 + 82 + 946 = 1035 7 + 82 + 964 = 1053 7 + 84 + 935 = 1026 7 + 84 + 962 = 1053 7 + 85 + 934 = 1026 7 + 86 + 942 = 1035 7 + 96 + 248 = 0351 7 + 96 + 428 = 0531 7 + 98 + 246 = 0351 7 + 98 + 426 = 0531 8 + 26 + 479 = 0513 8 + 26 + 497 = 0531 8 + 27 + 496 = 0531 8 + 29 + 476 = 0513 8 + 34 + 579 = 0621 8 + 39 + 574 = 0621 8 + 43 + 975 = 1026 8 + 45 + 973 = 1026 8 + 46 + 297 = 0351 8 + 47 + 296 = 0351 8 + 56 + 179 = 0243 8 + 57 + 169 = 0234 8 + 59 + 167 = 0234 8 + 59 + 176 = 0243 8 + 64 + 279 = 0351 8 + 67 + 159 = 0234 8 + 69 + 157 = 0234 8 + 69 + 274 = 0351 8 + 73 + 945 = 1026 8 + 74 + 269 = 0351 8 + 74 + 539 = 0621 8 + 75 + 943 = 1026 8 + 76 + 159 = 0243 8 + 76 + 429 = 0513 8 + 79 + 156 = 0243 8 + 79 + 264 = 0351 8 + 79 + 426 = 0513 8 + 79 + 534 = 0621 8 + 96 + 247 = 0351 8 + 96 + 427 = 0531 8 + 97 + 246 = 0351 8 + 97 + 426 = 0531 9 + 26 + 478 = 0513 9 + 28 + 476 = 0513 9 + 34 + 578 = 0621 9 + 38 + 574 = 0621 9 + 56 + 178 = 0243 9 + 57 + 168 = 0234 9 + 58 + 167 = 0234 9 + 58 + 176 = 0243 9 + 64 + 278 = 0351 9 + 67 + 158 = 0234 9 + 68 + 157 = 0234 9 + 68 + 274 = 0351 9 + 74 + 268 = 0351 9 + 74 + 538 = 0621 9 + 76 + 158 = 0243 9 + 76 + 428 = 0513 9 + 78 + 156 = 0243 9 + 78 + 264 = 0351 9 + 78 + 426 = 0513 9 + 78 + 534 = 0621