2, 3, 5, 6可以组成多少个四位数答:2356,2365,2536,2563,2635,2653,3256,3265,3562,3526,3625,3652,5263,5236,5326,5362,5623,5632,6235,6253,6325,6352,6523,6532.一共24个
用1、2、3、4、5、6可组成多少个没有重复数字的四位数?答:先组成15个基础四位数:1234,1235,1236,1245,1246,1256,1345,1346,1356,1456,2345,2346,2356,2456,3456 然后,每个四位数分别有24种可能排列,所以一共是24*15=360个