9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
9 - 3 = 6 vậy có các số: 93; 39
8 - 2 = 6 vậy có các số: 82; 28
7 - `1 = 6 vậy có các số: 71; 17
6 - 0 = 6 Vậy có số 60
Có tất cả 7 số có hai chữ số mà hai chữ số của số đó hơn kém nhau 6 đơn vị.
