总共427次=================================一千以内0在个位:10,20,30,40,50,60,70,80,90--9次*10=90次整百:100--2次*9=18次零在十位:101,102,103,104,105,106,107,108,109=9次*9=81次一千到两千:1000--3次1001,1002,1003,1004,1005,1006,1007,1008,1009--18次1010,1020,1030,1040,1050,1060,1070,1080,1090--18次整百:1100--2次*9=18次...展开总共427次=================================一千以内0在个位:10,20,30,40,50,60,70,80,90--9次*10=90次整百:100--2次*9=18次零在十位:101,102,103,104,105,106,107,108,109=9次*9=81次一千到两千:1000--3次1001,1002,1003,1004,1005,1006,1007,1008,1009--18次1010,1020,1030,1040,1050,1060,1070,1080,1090--18次整百:1100--2次*9=18次零在十位:1101,1102,1103,1104,1105,1106,1107,1108,1109--9次*9=81次零在个位:1110,1120,1130,1140,1150,1160,1170,1180,1190--9次*9=81次2000--3次两千以外:2001,2002,2003,2004,2005,2006,2007,2008--2次*8=16次总共=90+18+81+3+18+18+18+81+81+3+16=427次收起 |