9999
24
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
840
There are 3024 of them.
256 numbers.
24 different numbers.
There are 34 = 81 numbers.
Without repeats there are 4 × 3 = 12 possible 2 digit numbers. With repeats there are 4 × 4 = 16 possible 2 digit numbers.
There are 3 values (1, 2, 3) for each of the 4 digits. Therefore, there are 3*3*3*3 or 81 four digit numbers that can be formed.
24
24
Any 3 out of 4 = 4. Each set can be arranged 6 ways so 24 different numbers.