For any of nine first digits, you can chose from the eight remaining digits for the second number 9*8=72 different two digit numbers UNLESS You're willing to ... you define repetition. do you mean not repeating the same digit i.e. read more
Thus for the 2 digit number you have constructed so far there are 4 4 = 16 choices. Now write down the third digit. Again there ae 4 choices so the number of possible 3 digit numbers is 4 4 4. read more