Answer:
56
Step-by-step explanation:
If there can be only one 1 and only one 2, the remaining digits must all be 0. The digits 1 and 2 can be anywhere in the 8 digits, and can be in either order.
There are 8 possible locations in the sequence for the 1, then 7 possible locations for the 2. The total number of possibilities is 8·7 = 56.
12000000, 21000000, 10200000, 20100000, ..., 00000012, 00000021.
