19 times
10,11 (is 2),12,13,14,15,16,17,18,19,21,31,41,51,61,71,81 and 91
8 of them.
With 123 digits you can make 123 one-digit numbers.
How many times does the digit 1 occur in ten place in the numbers from 1 to 1000?
16000
about... 25 just take 5 numbers times 5 numbers
12 numbers
Not sure what a "didget" is. It is possible to make 18 5-digit numbers.
11 times
As a digit in other numbers it appears 20 times
8
The digit 3 will be written 20 times.
Infinitely many.