各位數字的和是等於24

一定不會有1-5
所以有
699, 969,996
789, 798, 879, 897, 978, 987
888

Delete the number:
1+9+9=19
...
5+9+9=23
6+9+8=23
so 699 is right.

Delete:
7+0+0=7
...
7+7+9=23
...
7+8+8=23
So 789,798 is right.

Delete 800-869
870-878
880-887,889
890-896,898,899
So 879,888&897 is right.

Delete 900-959
960-968
970-977,979
980-986,988,989
990-995,997,998,999
So 978,987&996 is right.

Hope I can help U.