✔ 最佳答案
試下咁分:
(A)1 --- 共1個
(B)10-19 --- 共10個
(C)21, 31, 41, 51, 61, 71 81, 91 --- 共8個
(A) + (B) + (C) 共19個
(D)100 - 199 --- 共100個
(E)201, 210-219, 221, 231, 241, ..., 291, 301, 310-319, ..., 991
--- 共8*((A)+(B)+(C))=152個
(F)1000 - 1999 共1000個
(G)2001, 2010, 2011, 2012, ..., 2019, 2021, 2031, ... , 2091, 2100, 2101, 2199, 2201, ..., 2991, 3001, 3010, ... 9991 --- 共((A)+(B)+(C)+(D)+(E))*8
= (1+10+8+100+152)*8 = 2168個
(H)10000 --- 共1個
所以1至10000, 總共有((A)+(B)+(C)+(D)+(E)+(F)+(G)+(H))
= 1+10+8+100+152+1000+2168+1
= 3440個