There are 2892 digits.
2625
There are 120 of them.
How many strings of three digits are there? 000 to 999, or a total of 1000. How many strings of three digits contain the same three digits? That's 000, 111, 222 ... 999! ten in total. The difference is your answer: 1000-10 = 990.
123
Not couting 1 and 1000, there would be 998 numbers.
648
10 digits.
How many
252 of them.
10000
There are 125 of them.