Infinitely many.
As a digit in other numbers it appears 20 times
18
18 times
A total of 44 times.
20000 times
11 times
As a digit in other numbers it appears 20 times
18
Assuming you mean in the numbers 1, 2, 3, ..., 998, 999, 1000 then the digit 0. (The digit 1 appears 301 times, the digits 2-9 all appear 300 times each, but the digit 0 only appears 192 times.)
18 times
A total of 44 times.
20000 times
200
200
16
140
700000