three (111 + 111 = 222) or four (999 + 999 = 1998)
With 123 digits you can make 123 one-digit numbers.
7 two-digit numbers.
There are 9 digits that can be the first digit (1-9); for each of these there is 1 digit that can be the second digit (6); for each of these there are 10 digits that can be the third digit (0-9); for each of these there are 10 digits that can be the fourth digit (0-9). → number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.
None. 3 digit numbers are not divisible by 19 digit numbers.
500
With 123 digits you can make 123 one-digit numbers.
There are 5460 five digit numbers with a digit sum of 22.
27 three digit numbers from the digits 3, 5, 7 including repetitions.
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
757
There are 90000 5-digit numbers.
7 two-digit numbers.
There are 9 digits that can be the first digit (1-9); for each of these there is 1 digit that can be the second digit (6); for each of these there are 10 digits that can be the third digit (0-9); for each of these there are 10 digits that can be the fourth digit (0-9). → number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.
None. 3 digit numbers are not divisible by 19 digit numbers.
500
24
840